to ask other people to get their DC to sit down and be quiet?

[AlmondAmy]

My eldest does an after school activity which you can watch from a viewing gallery in an indoor sports hall. I take my 2 yo and new baby with me and take books and snacks to keep her busy. The other parents with younger siblings let them run around, up and down the front of the seats and on the stairs, as well as letting them make as much noise as they like.

Luckily my DD is happy to sit down and not join them but their noise and running is distracting for the children doing the activity and they often struggle to hear the teacher over the noise from the viewing gallery. Also, the activity is at my babys nap time and though we sit as far away from the others as possible they still keep running and shouting near us and waking her up. Aibu if I ask the parents to try and encourage their children to sit down and be quiet next time? They are all aged 3-7 so older than my DD and capable of sitting quietly.

*should be past

Not all young children are willing to sit quietly for protracted periods of time. Books and colouring only works for a short while with some children, you're fortunate it occupies yor DC for so long.
Ynbu to wish other children could sit as quietly as yours, but I imagine a few of the parents wish the same!
Yabu about your napping baby and to think that you can ask everybody else to maybe do the impossible.
If it causes such a problem for the activity the teacher should address it and perhaps the only option would be to ban the audience.

Just to clarify I'm not in favour of children being allowed to run wild, I would be expecting the other parents to be parenting not ignoring. However, it is just not always possible to get children to sit down quietly for longer than than ten minutes.