Several well-situated British country estates have taken on a startling new guise: at-your-service hotels expressly set up for families. At each of the Luxury Family Hotel group's locations (; doubles from $139, children free), kids can check into a well-stocked playroom staffed by nannies. There's also Nintendo, as well as biking, swimming, tennis, riding, and acres of grounds to explore. Guests at the just-opened Ickworth House, a National Trust property in Suffolk, 75 miles northeast of London, often spend an afternoon punting in Cambridge. Woolley Grange is minutes from Bath. And the Cornish seaside mansion Fowey Hall is a short drive from the Eden Project. Each hotel has a "baby listening system," designed so parents can dine in-house while kids slumber. —Erika Lederman