Personally I love living in London. So many people told me I'd feel differently and want to relocate to the country once I had kids, but they were wrong! I have a dd (age 2) and another on the way and have just bought a new house in SE London. We live in a wonderful community - rarely have to go to a supermarket because the local shops are so good. Virtually never get in the car because we can walk everywhere or use public transport.
There's so much going on. Admittedly we don't do as much theatre, concert, cinema and opera as we used to (let's be honest we hardly ever go these days!). But we'll pick that up again when the kids are bigger. And for us the biggest thing is that so many of our friends are here, and we have a lovely lifestyle.
I grew up in rural mid Wales, but now I wouldn't swap city life for anything.
The only thing I don't enjoy is the length of my commute, but that's because I often end up working in different locations and travelling an hour and a quarter to an hour and a half each way. When I'm working in central London and can get my commute down to 50 minutes I find it's fine. The trains will be busy in from Blackheath, but I guess you know that.
Good luck with the decision