No idea, sorry - I live about 10 miles away though :)
DD2 will enjoy the Adventure Wonderland at Hurn, opposite the airport. Might be a bit young for the older girls.
They'll probably all enjoy Splashdown at Tower Park - all water slides, nearly all indoors. Bit pricy, but very worth the money if you like that kind of thing. There's a cinema and bowling alley on site too.
Surfing lessons at Boscombe beach?
I can thoroughly recommend the Raptor and Reptile Sanctuary between Ringwood and Poulner - fantastic place, and a lovely coffee shop. I last went a couple of years ago but have been promising DP a trip - it suits all ages.
Lots of riding stables around which will offer beginner hacks across the Forest.
New Forest Museum in Lyndhurst for the obligatory history lesson, plus the real Alice in Wonderland is buried in the parish church just up the road. Walk about half a mileout of town down the A35 and the Swan does lovely food.
Picnics and walks in the New Forest. Hatchet Pond and Wootton Stream for paddling. Wilverley Plain for kite flying. Beaulieu for classic cars and donkeys wandering around. Lymington or Christchurch for fish and chips on the prom and a goggle at the little boats.
For the witchcraftery-minded, Burley is great fun - afternoon tea and a wander round the hippy shops, with ponies in and out of the traffic...
Both Hengistbury Head and Hurst Spit have ferries, so if you fancy a walk but small legs can't quite manage, maybe walk to the end and get the ferry back (used to do this with my Gran, or we'd meet her at the end for a cuppa)
HTH??