Mrs DTK - really please to hear of your housing transfer - sounds excellent. i did wonder whether your DS was a member of the Incredibles family when you said he walked to school in 10 mins when he first started! It sounds as if he's doing really well - good for him - DS will go in 2012.
Great tip about the park.
I have met MrsDTK at least twice and she is indeed fab. She organised the MN Mile For M walk in a local park, too, some years ago! I think providing a network of helpers for each other's vulnerable relatives across the country sounds a lovely idea!
I wonder if the siting of a specialist unit for young people removed from school in W Norwood is a factor? 
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In all truth, I think community and knowing people is a lot about making yourself feel at hoe wherever you live. I never wanted to live where I do, but as Kirsty says, you have to compromise to budget, and in terms of access to transport, parks, good schools, and hous pices we couldn't get a better mix in our budget. And having oved here i am really pleased to find that we are in a close knit community of other families in the local roads, from school, and with a great community spirit.
I also found that in Brixton, I know MI enjoys that in Catford - and all areas of London have little micro-climates - the property-porn haven cheek by jowl with bleak dereliction. You can't generalise about areas. OP, I would identify what suits your commuting and schooling needs first and then look at property in residential family-orientated roads..