We've been to Ightham Moat a couple of times now and enjoyed it both times, although they have felt quite different visits, with the first being back in October 2017 with 10-year-old twins and then the next time was this summer, during the COVID pandemic, and we took our three teenagers.
If you're looking to visit in the near future the moated house is currently closed but you can enjoy the outdoor space, both the gardens and the wider estate. The gardens aren't too big and with a one way system currently, they will only take an hour or so to walk around. If I'm honest, they are not impressive like the gardens of many National Trust sites. I think the gem of this site is being able to go inside the house, so with that closed the site doesn't have quite so much wow factor as normal. However, if you are willing to head out and take a longer walk, then the wider estate is fabulous and well-worth exploring. There is a big hill though, so be warned!
I think pictures speak a thousand words, so have a look at these from our visit this summer. The first few photos are within the gardens.