Planing our 2019 trip !

If you don’t want heat and humidity then definitely stay away from Southeast Asia. I would also nix southern France and the Adriatic because of the heat and humidity. The London, England and Scotland would be better and give you the variety that you are looking for. Or perhaps Scandinavia.

Maybe people have given wrong information, but some people have told me that southern France weather is not bad since is mostly dry heat.

I am a teacher, too, so have traveled every summer. After 100 + degrees in southern Spain a few years ago I flew back to the US via Iceland as a several day stopover, primarily because of the cheap airfare. A revelation! Your kids are the perfect age for new adventures, how fortunate to share them together as a family. This past summer I had 3 weeks and explored Norway, Finland and Copenhagen ( are they into Legos?!). Iceland Air has packages for the stopovers of various lengths. My next trip I hope to explore northern Scotland and Ireland and Greenland. So stay north! ( p.s. Australia might be too $ and far right now, but I did that, too- it's their winter!)

I guess it depends on what you are most looking to do. For mountains and then some villa life, your Italy plan sounds lovely. For some sea and culture, your France/Spain option. My top choice would be London and Scotland. I have not been to the two remaining locations, but would choose Croatia, Bosnia, and Slovenia if I needed a new place to visit. Sorry this was not super decisive as they all sound great. If you polled the kids about what they would like to do (open ended without specifying the locations), I wonder if their response would narrow it down or at least give you ideas of things to throw in once you make a decision.
I'm a school psychologist too!

Forget Asia - that's madness if you don't want lots of heat/humidity.

If you want Europe, then you need to look at: United Kingdom, Ireland, any of the Nordic countries (Scandinavia, Iceland), or the Baltics. Maybe along the norther parts of Germany/Poland. You could still get caught in a heat wave (ask anyone who was in the UK during July this year...) but odds are, you should enjoy relatively mild weather in any of these places (possibly some wet and cool weather, too - which sounds pretty good right now from this guy sitting in Seattle...).

We visited South of France the first few weeks of July this year - and while it was really really hot (upwards of 35C every day - a few times the car thermometer read 40C) I did find it more of a dry heat, as you mentioned - compared to the humidity we've had here this summer. But it was still a bit hard dealing with it - we were lucky that we had a car, so retreating to the AC in the car was a blessing. I did find after returning home and dealing with excessive humidity a lot worse though. We did lots of water and slushies. But the time of year - with the lavender fields in bloom - was amazing, and many of the smaller towns and villages weren't that busy. And if you stuck to southern France, you could maybe rent a Gite for part of the time, with a pool to help keep cool. But make sure where you stay has AC - one of our airbnb's didn't have AC, they said it didn't get that hot - but it was hard to sleep - luckily the windows had screens (a rare commodity it seems) so we could keep the windows open for a breeze, but keep the bugs out.

And don't forget the changing weather - England suffered thru a heat wave this summer, and they don't have the AC to help fight it. And Spain was crazy hot as well.

July/August is the best time to see Scandinavia. It's when you will get the most reliably nice weather.

Probably the most reliably good weather in UK also.

It's the best time to visit San Sebastian/Donostia, Santander, Bilbao - the north coast of Spain. It's rainy and cool most of the year but gets very nice in the high summer season. I was there in April, it was rainy and quite cold.

The coasts of Normadie and Brittany should be pretty nice too. They tend to get rainy and chilly outside of high summer months. I visited in early September and it was really nice.

The high Alps are best in the main summer months. It's probably better to plan later in case the trails still have snow pack on them. In France, mid-September was beautiful. In Germany, mid-October was freezing and very little visibility.

Southern France, Northern Spain, and Italy/Tuscany will all be hot. I'd expect the same in Croatia, Bosnia, Slovenia. I haven't been to Hungary yet, typically inland areas get hot in the summer and cold in the winter because there is no ocean moderating the temperature. Provence was still quite hot when I was there in mid-September, which was nice when I then went to the Riviera. Coastal areas aren't bad because you can jump in the ocean to cool off (but there are lots of jellyfish along the French Riviera then).

Southern Croatia in July and August is likely to be as hot as southern Italy unless you head to Istria in the north, which could be combined with Slovenia within your timeframe.

Your children may find the UK easier if they only speak English - it’s useful to have some Spanish if you are heading to rural northern Spain. The south of France is too busy for my taste at that time of year.

The Italian Lakes can be quite wet compared to say the Algarve in Portugal.

We were southern France in July 2015 because I wanted to see the lavender fields in bloom. Trust me when I say it was unbearably hot and I live in the desert. Dry heat or humid heat makes no difference. It was hot and very uncomfortable but I wanted to see the lavender and that was something I was willing to put up with to see it. We needed to change our clothes twice a day and were grateful for ac in the car and hotels and swimming pools at the same. I did a lot of laundry while we were there.

Iceland is great for kids (and just about everyone!) You might consider Basque France and Spain. That area is cooler in the summer than other parts of Spain. Absolutely phenomenal would be Switzerland (Luzern, Berner Oberland are my favorites, but also worth consideration would be Basel, Bern, and Montreau/Lausanne)

If you want to stay away from heat, I would either do Scandinavian countries or England, Ireland and Scotland. Our very favourite family trip was a 2 week our Ireland when our kids were 8 and 11

All the times I have been to southern France were in the summer, ie in July. The first visit was in 1997 in Toulon, Avignon, etc. True, the heat and humidity were admittedly a shocker with the temperature, the proximity to the Mediterranean, and the latitude. The next occasion was in July 1999, this time I was more prepared to handle the weather.

If you decide on China, better to go in Sept/Oct rather than in the summer.

We enjoyed 2 weeks in northern Spain in July. We spent a week in Galicia and the weather was very pleasant. With 3 weeks you would have time to see the basque region and places in between.

The stretch of northern Spain from the Basque Country in the east to Galicia in the west may be the most affordable European option for a mid-summer trip with little risk of high heat. There are a bunch of really interesting cities in that area. Some of them are far enough from the coast that they are in a different climate zone, so you should check weather stats for any non-coastsl cities before planning multiple-night stays there. Santiago de Compostela is fine; it is notorious for its overcast skies.

The Picos de Europa is a dramatic mountain area near the coast.

Possibly the second-cheapest option would be Normandy and Brittany in France.

1) London can be warm in summer so you would want rooms with AC - and London's expensive. On the other hand, Scotland is rarely hot, neither is Ireland. And they are easy on the budget, with lots to see and do. The only consideration is that there's not much of a train system in Ireland - though there are good connections between Dublin and Belfast, Cork and Westport. A big plus is that English is the local language, so every activity will be in English.

Based on your past experience and the time of year your #1 choice is the obvious answer.