What would you recommend- short trip!

It all depends on what your children, and yourself, like. Also, it sounds like your goal for this trip is to introduce European Travel to your children.

You should be aware that the Edinburgh Fringe Festival runs from Aug 5-29 and my understanding is that accommodations are scare and expensive during this time. If you haven't started your search yet, you may find this an issue.

Perhaps go from Glasgow directly to Oban. and base there for 3 nights. Staffa closes in mid-August, but there are other islands to explore as well as Oban itself. Skip the Ocean Explorer Centre. This is a must-miss activity.

Then go to Edinburgh area at the end of your trip when lodging might be more available or reasonable. A fun day trip from Edinburgh is to go to St Andrews where the entire family could play on the Himalayas putting course which is a great deal of fun and located directly next to the Old Course. The beach there is the beach from the theme song in "Chariots of Fire" which might be a fun movie to watch as a family prior to your trip.

If Edinburgh is still full or priced out of reasonable range, consider Stirling where you can tour the castle (which I liked better than Edinburgh Castle anyway) and you aren't far from the Falkirk Wheel. The Falkirk Wheel is set up for family fun and exploration.
https://www.scottishcanals.co.uk/falkirk-wheel/

I would not try for more than 2 bases with this time period.

I am definitely not an expert here but have been researching (and reading through this forum) for a trip next spring to Scotland. One option I was thinking of is the Isle of Arran. From what everyone has been saying, it is considered a "miniature" Scotland because it has all the features of the country contained on a small island.

The nice thing is that it is not that far from Glasgow, so you could easily rent a car from Glasgow and take it over to the island, stay for a few days and then head back to Glasgow and on to Edinburgh. I've listed a few links to posts below that talk about Arran but you can always search for more.

https://community.ricksteves.com/travel-forum/scotland/isle-of-arran-or-oban
https://community.ricksteves.com/travel-forum/scotland/arran-oban-oban-mull-or-isle-of-harris

Another thought might be in the Fort William area. You could take the cable car up Ben Nevis, drive over and see the Caledonian Canal and the locks, take a half day and ride the Jacobite steam train, take a short Loch cruise either right there in Loch Eil or a short drive to Fort Augustus for a cruise on Loch Ness.

My experience in Scotland is very limited, but quite near Glasgow is Glencoe. The kids might appreciate the outdoors there. There are trails, which are varied and easily accessible, and the difference between the urban bustle of Glasgow and the rural quiet beauty of Glencoe is striking. It might make for a good day on your way to Oban or the other spots recommended by others here.

You are going to struggle for accommodation in Edinburgh during August and also at many coastal locations, as it is school holiday time. If you can’t find accommodation in Edinburgh, it’s only an hour from Glasgow by train for a day trip.

The North Ballachulish area would give you access to Glencoe for walking and take a cable car ride, take a ride on the short ferry crossing from Corran to the Ardnamurchan peninsula and go looking for otters and wildlife and visit the lighthouse and have a day trip to Oban or Ben Nevis. You need proper equipment and footwear if climbing any of the mountains.

I'm a big fan of Mull but it's a long drive from Edinburgh and once you're there it's a slow drive to get anywhere. I wouldn't call it kid friendly. I'd stick to Edinburgh and do some daytrips including Stirling Castle.

Throwing out a different idea. You could expose your kids to 2 counties and split your time between Edinburgh and York, England.

I'm a big fan of Arran. It would give your kids a nice taste of a ferry and what the highlands are like. They can beachcomb in any number of places, clamber around castle ruins, maybe try a round of golf (I think there are 9 courses), and see standing stones. I also like the idea of North Ballachulish. Close to Glencoe and Fort William and the village of Kinlochleven which has the Grey Mares Waterfall and the National Ice Climbing Center. Which not only has the highest (I think) indoor ice climbing wall but also rock climbing and an aerial course. I think it's open to the public but you would need to double check. https://www.ice-factor.co.uk/

Do your kids like Harry Potter? If yes, the previously mentioned Jacobite train is what you need to take if you can still get tickets. It's the train used in the Harry Potter movies. Its a beautiful ride.

Additionally, the train from Glasgow to Fort William is one of the most scenic in the UK.

Many thanks, all! So many great ideas, saved some for the next time also.

Looked through all of your great ideas with my husband and decided upon Isle of Arran. Hotel booked! I had heard of it a bit, but it really seems to be the perfect option for this short trip.

Thanks again- will update after the trip with how it went!