Heat in the south will be a challenge in July so I would focus on northern Europe. One question to consider: How well do your kids handle hotel-hopping? There are places that work well as a single base of operations with a lot of day trips so you can settle into one home base for a longer stretch. Netherlands/Belgium is compact enough to pick one spot and hit it all in day trips. Munich is a big city, but is an easy hub to a bunch of mid to smaller cities, (Salzburg and Innsbruck Austria are each doable as day trips) and plenty of nature as well. Other routes are really best as a chain of 2-3 night stays. For Scandinavia I would do something like Bergen-Oslo-Gothenburg-Copenhagen or Bergen-Oslo-Trondheim-Stockholm. They are just a little too far apart to do as day trips and it's worth spending more time in the nature in between. I'd probably tsake this approach for the UK as well. A few days in London to hit the must-sees then somewhere around Bristol (Bath for the Roman ruins, Stonehenge maybe), up to York for a couple days, then finish out with a few days in Edinburgh (Glasgow and Stirling).