How old are your DC's? You will be in almost the heart of Camden, which isn't exactly child friendly in itself, but fine for little ones who won't be wandering around by themselves 
- teens I would think twice about. Lots of young families around but not at all "nappy valley" like some bits of London.
There are loads of Surestart things in the library at Crowndale, (opposite Mornington Crescent tube) and also private activities. Some great sports and leisure centres very close by (Talacre, Swiss Cottage, Kentish Town sports centre) and of course Regents Park, London Zoo, Primrose Hill. Hampstead Heath is 15 mins away on the bus, also all the museums in South Kensington (Science, Nat History, V&A) just a tube/bus ride away as is the Southbank and all of central London. It definitely feels like London proper, but you are within easy reach (less than 10 mins walk) of the open spaces of Regents Park.
A good primary and one you should fall into the very small catchment for is Hawley Infants School - a lovely, non religious state school. It has one class per year up to year 2 (then children go on to Primrose Hill Primary/Barrow Hill in St Johns Wood or others). No uniform, children address teachers by first name - motto is "a village school in the heart of Camden" - which is how it feels. Very nurturing and friendly. There are plans to build a new Hawley School just around the corner which would include junior school so avoid the need to move school at 8. Not sure of timing though.
Another good primary in the area is Holy Trinity & St Silas which is CofE and very good (appeared in top 20 state primary schools in the Times list a few weeks ago, if that's important to you)- not easy to get into though, esp if you aren't a churchgoer. Primrose Hill Primary also nearby and good but headteacher has just changed and it is much bigger than the other two I mention.