Hever Castle is surprisingly child friendly. I tend to steer clear of castles and stately homes, fearing the toddler will do expensive damage to the tapestries or fall into the moat, but Hever goes out of its way to welcome children. It is a nicely compact castle and grounds - much smaller than Leeds Castle. It's full of interest with just enough to keep everyone happy for a long afternoon.
Adults get award-winning gardens, including a lovely Italian Garden, and a very well stocked plant shop.
Children get an adventure playground, with enough equipment to suit toddlers and older children for an hour or so.
They also get not one, but two mazes. The first is your typical yew maze. Our 7 year old thoroughly enjoyed being the leader in and out of it - indeed, most adults were being lead by excited children.
The second maze is fantastic and totally unexpected. It is a water maze. By treading on large stone slabs, you may or may not set off fountains. These are meant to block your way, so you turn back and go by another route. However, on our visit, the hot sunshine meant children far preferred getting soaked. Good idea to take a change of clothes.
It is suitable IMO for older toddlers, as long as you don't mind following close behind and getting a little splattered. The stone slabs are set very close together in a shallow lake - the water is under 2 feet deep. I was amazed to see some biggish toddlers sitting and watching the fun from a distance on their parent's laps. My toddler wouldn't have stood that for a minute. I carried him, running, through the fountains or followed close behind him. I did sense a few 'looks' from some of the sitting toddler parents, but equally some parents were doing as I did. Anyway, I'm rambling.
The castle tour is interesting and takes just 20 minutes. I didn't try the restaurant, but the cafe sold good food, especially the great home made cake selection - and was nicely inexpensive.
Hever castle is an easy drive if you live in SE London, like me. It is 20 minutes or so off junction 5 or 6 off the M25. Definitely worth a visit.