The Divine cafe at Cherhill like Mikes suggested is really nice, but not too sure the food is what most kids would go for its really? Its not a chips and burger sort of place. Some lovely open roads around it - the A4.
Depends a lot of what sort of roads you like and how far you like to go.
If you venture to the coast Poole, Studland and West Bay are good. West Bay is very popular with bikers and lots of little huts selling chips on the front right next to where you stop with a bike.
A circular route going across the chain ferry at Studland makes a nice run and a bit different going across a chain ferry.
