Hi there
I've been thinking a bit about this. Just picking up on some of the things you say in your email:
'less crime and grief on the streets'. Well, yes (I used to live in the East End and its definitely less threatening here) but it's not entirely peaceful - Cambridge has a very large population of homeless people, which does bother some inhabitants. Still, I think you'll probably feel more secure here.
'access to cinema'. Tick. No problem. One Warner multiscreen, one good Arts Cinema and another multiplex being built near station.
'better schools' I think Tigermoth, Babster and Popperoo have summed it up - my little guy is well under school age so its not on my radar.
'More playgrounds'. Dunno how many you have in mind - I live 10 minutes walk from the station and can think of two good size playgrounds and 2 large parks within 15 minutes walk.
'Commuting' Bit tricky to comment without knowing your planned route. As I mentioned below, I went to the West End every day for 9 months and it's not the worst commute in the world but you're at the mercy of WAGN - do yourself a favour and check out their service record recently.
'feeling isolated' No more a danger here than in London, I would have thought. Can't guarantee instant replacement for kids friends though!
Property prices. Have been going up rapidly for ages and are due to slow down, but who knows? If DH is commuting and you want to be near station that could be interesting - on one side of tracks you have 'nicer' area with larger, more expensive family housing - on other (where I live) smaller terraces which are more affordable - 150-200k -but will be a bit of squeeze with two kids.
Stuff to do. My guess is you might find yourself on the train a bit! London much better for museums and dry days out for small kids.
Sports facilities adequate, not outstanding - off the top of my head I can think of tennis courts, real tennis, climbing wall, three swimming pools plus one outdoor pool and a paddling pool, lots of gyms, several cricket/sportsfields, numerous rowing clubs, squash courts and a model railway club with outdoor track.
The downside of living here is that the surrounding country is really not that exciting for recreation. There's sailing within 30 minutes at Grafham, some easy family walking and cycling with good pubs etc, but if you like hill walking, riding or anything more strenuous then you'll spend a lot of time out of town!
OK I warned you about the rambling but there you go.