That seems reasonable enough - allows the kids to let of steam whilst taking into consideration the school is in a residential area.
There's actually a school that I think does similar near where I work - if I hadn't happened to walk right past it one day and spot some children in the playground, I'd've never known it existed. Unlike the one near the doctor's surgery - you can hear them a reasonable distance away at playtime (although my main gripe with that school is the parents - but this isn't the vent and rant thread
)