I think there are tons of times where you can see parents perhaps being harsher than you think necessary but you don't know what's come before it - little Johnny could have been an utter toad all day and that one final act pushed mum/dad's patience over the edge.
This is exactly why I didn't say anything. But I was still

I'd have said something to them, even if it was a simple "it's okay, I don't mind them coming near me"
Did this, several times. I was smiling at the kids, half playing with them, told the parents they're really well behaved kids.

I think I might bring it up with someone else. I know they have a play room for kids that are noisier, but for the most part the congregation are a pretty clucky bunch and happy with the kids just playing on the rugs. The only announcement they've made about babies/kids is that if they're crying/screaming to please take them out.