We also moved for an affordable house and good schools. At first HOP felt a bit quiet compared to other areas but now I love it for that. There's a real community feel, lots of young families and green space - and yes, plenty of children hiding, so take a look at just before 9am or just after 3.30pm and you'll see the crowds to and from Stillness, Dalmain and Fairlawn! I'm very happy my children live in this area - our street is safe and friendly and there are plenty of activities going on. You might need to seek them out a bit more than ED, though.
Places that haven't been mentioned for you to try...
One Tree Hill (great views, great for blackberrying, sledging and summer picnics) and the Honor Oak Sports Ground, known as the Rec (take the turning next to the allotments and keep going - you'll find a little playground and a big sports' field).
Devonshire Road Nature Reserve is open on the last Sunday of every month and also has lots of special activities for children throughout the year.
Decent pubs are a bit lacking - but hoping that will change with the Old Bank!
Good luck with your decision. I'm sure you won't be disappointed!