I was cutting grass at 12 years old on the weekends during school year and then summer time washed cars and cut grass. Only did it until I was 14, where I got a part-time job as a bagger and cart pusher at a grocery store. Don't see a problem with it.

Edit: I'm from the U.S. though.

I was working summer jobs doing farm labour since before I was a teenager (and I'm not that old), so I'm gonna say that it's fine that 13 year olds are working.