Speke Hall

The actual house is probably only of interest to older children and adults, however they do lots of family events.
The grounds are fab, beautiful gardens and a very good enclosed play area. Lots of picnic opportunity. The big bonus for Speke Hall if you have young children is that you can walk through the wooded area of the grounds along side the airport runway so you can see the planes land and take off.

If you want to eat there I suggest a picnic as the cafe is expensive.