Children around my home play out until all hours, especially in the school holidays, and can be quite noisy.
I don't mind at all because I love to hear them enjoying themselves, even at 8 or 10pm.
I wouldn't say you are being unreasonable to feel the noise is an intrusion, just that you haven't yet learned to manage living in a community with children.
Turn up your radio or TV, use earplugs, be glad they are playing and enjoying themselves rather than screaming in fear.
Community life is all about compromising and you can always ring Noise Control if, after midnight, they are still making a racket.