I’d put a 2nd on Wales. Not sure where you’re based, but plenty of options whether your looking for countryside / mountain / forest escape or something a bit more coastal. We’re open all year. Be sure to bring a jacket though for everyone, and a pair of wellies and you’re away.
We also just spent some weeks this summer driving down through France. Not a bad trip and a pretty easy going place for that.
Plenty of cheese and bread to keep our little one happy!