I just looked up Forest Holidays..... ¬£2,900 for 7 nights August , log cabin, Beddgelert ! So basically, it's self catering under wood and in a wood.
Tent in a wood sounds much better.
Depends on age of kids. Shropshire has quite a lot of interesting places. Otherwise I'd suggest N. Wales. Lots of beach in Llandudno, Zoo &, swimming baths at Colwyn Bay. (All extra cash of course) https://www.tripadvisor.co.uk/Attractions-g186365-Activities-Shropshire_England.html