I holidayed in Poolewe for a few years. It’s very pretty but your kids boredom will drive them to hate you forever.
Without a doubt the best place north of the Tay that matches your needs is Aviemore.
Consider Fife for anywhere South of the Tay. It has everything close to hand but also some seriously bonny neuks.
Consider the borders if you’re cool with Tories and endless rain.