I'm not sure what you mean by "caters well for children" - do you want all singing, all dancing with pool and everything or just a play area?
The Beddgelert Forestry Commission site is lovely. It's in the forest and about 15 minutes walk from the village. There's a playground for the kids but that's all.
From Snowdonia you can easily get round a lot of North Wales and there's loads to do. Why don't you Google the tourist information for the area.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.