Alternatively, you could leave the mainland and head over to the Isle of Wight. Did my PB 2 and ICC with Dave Robson of Aquapower
(currently providing safety boat cover at the London Boat Show) and Richard did Advanced with him. He's based in Yarmouth and there's loads to do on the island - beaches, walks, zoo, funfair etc if the weather's good and indoor attractions too. The island's tourism site is here
You could save the ferry fare and take your own boat over - launch from Lymington/Calshot or similar and take an easy ride over the Solent to Yarmouth - really friendly & helpful harbour staff who can usually find you a berth.
Wherever you go, hope you & your family have a great time.