Spain for 8-10 days, not including Barcelona (in Winter)

I don't know anything about the Canary Islands, but winter would be a fine time to visit the cities of Andalucia (which can be scorching in summer). You can see typical temps on a website like Wunderground. The train system is excellent, but the itinerary would depend on where you fly in/out. Madrid is most likely, and it is well connected to Codoba and Sevilla by fast train, but I would definitely check the regional airports, Malaga, Sevilla, Jerez.

Las Canarias could be considered the "Hawaii of Europe", there is a lot of overlap with Hawaii in terms of things to do, lot of nature-y things. Not sure if that is what you are looking for. I'd only recommend Barcelona if the serious drought situation has been resolved by next winter, if not I'd hold off.

You could look at Andalucia or Valencia, both would be good around that time with a lot of festive cheer and Christmas markets, depending on when you go.

Madrid can be quite cold during the winter, it has the highest elevation of any EU capital, it occasionally snows there.

With 10 days you could hit Cordoba, Seville and Granada. You'd want to be at your departure city (which might be Madrid, but you can check Malaga, Seville and Granada as well) the night before your departure. Eight nights would be a bit tight if you had to fly out of Madrid or Malaga, but you could do it. Keep in mind that, though the weather will probably be decently warm, the days will be quite short.

Granada is at altitude, so it's likely to be cooler than Seville and Cordoba. I'd take a warm layer like a fleece jacket as well as a waterproof rain jacket--those are standard for me unless I'm visiting an area where the only weather risk is a heat wave.

If you really love Hawaii, Tenerife or another of the Canary Islands would probably be great for your family. Some very nice resorts and beaches are available there. I also spent the month of February 2023 in southern Spain, two weeks of which were in Málaga / Torremolinos, a week in Valencia and the remainder bouncing around among Córdoba, Granada and Madrid. Temperatures were mainly in the low to mid 60s along the coast, so no major beach time, but pleasant. Marbella is the city with IMO the finest beach scene and best oceanfront resorts.

We loved the Canaries. Weather there in the winter is likely to be very nice.

We flew I to Madrid and went immediately to Sevilla. Spent four nights there (with a day trip to Ronda). Three in Granada. One in Cordoba. One in Madrid before flying home.

Weather was 40-60 degrees in late December/early January.

It was packed. But we really enjoyed it!

@Jolie NC interesting to hear it was packed! This winter break, we did Venice and London. London was quite busy, but we only noticed when we went to the British Museum, because we’ve been there before and we otherwise weren’t doing super touristy things. Venice was pretty laid-back right up until the Friday before New Year’s Eve, at which point it became hard to walk in the streets and I was super glad I was not experiencing it at the height of summer.

I’m slightly surprised to hear that these cities in Spain are also really busy over winter break, but it seems like everywhere is busy all the time at this point! I kind of felt like one of the trade-offs for going in the winter was that it shouldn’t be quite as busy, and I’m sure it’s not quite as busy, but still. I am sort of leaning this way. I’m just thinking that the Canary Islands might be a huge pain to get to, and we won’t be that excited
when we are there.

@GeoffB thank you, I will check it out.

I can't speak to the Canaries (Canarys?) but it's no surprise that Anadalucia gets a lot of winter tourism since it's warmer than most of Europe -- to the point that it's too hot in summer for most people. And Madrid will definitely be cold because of altitude, though it might be your best airport for transatlantic flights.

Fast trains connect Madrid, Seville, Cordoba, and Granada, with Cordoba the "hub" for them all. A morning landing in Madrid gives you time to get to any of the other cities later that day, allowing time to get from MAD to Atocha Station in the center. For the "white villages" you would need a car. Jerez and Cadiz are interesting cities near Seville, I think reachable by train and certainly by car.

One advantage of flying into Málaga from the US is that airfares are often pretty low. Something to at least look into.