Where for a family weekend away not too far from London by train?

[IlanaK]

DH can't take any days off so would have to go Friday evening and come back Sunday evening. So short train from London. Not too pricey but maybe a hotel with stuff laid on for the kids (3, 7, 10).

Any ideas?

Rochester? Really pretty high street, castle, cathedral and museum, great Italian restaurant, but no kids club type things - you'd have to entertain them yourselves iyswim?

Thanks. I was hoping for specific hotel recommendations if possible!