If they are quiet and well-behaved, not an issue. I couldn't care less that they are children. There are nuisance people at any age anyway.

But if they are disruptive, I do not like it, but there is nothing I can do other than wearing whatever I have to block out the noise etc. Sadly too many flights have been adversely affected by disruptive passengers (mostly children, admittedly - but I blame their parents who made no attempt to manage the situation). However, well-behaved ones are totally fine. If they are really well-behaved, I shouldn't even notice they are there anyway.