My toddler was just a bit fed up of travelling not silently sitting on the plane. She was a bit loud and excited at times. At times we had to keep telling her to sit down as she tried to stand on her seat. There were many other kids making noise too. We did our very best to keep her quiet and keep her happy. She cried occasionally and occasionally made some noise. It wasn't excessive but the amount you'd expect when there's a small child on a plane.
I noticed people looking and didn't feel like apologising because it was nothing extreme and also she wasn't encroaching on their space.
The man in front of me reclined his seat immediately before we even took off. So I didn't think he deserved any kind of apology about my kids making some noise occasionally.
Also, we were doing our best. We were not ignoring our children or allowing bad behaviour. So I don't see what I need to apologise for. I just ignored the looks but felt like they may have expected an apology. I could be wrong of course.
I have apologised in the past for my kids. If they've kicked the seat in front of it they walk into someone's path etc. but I don't think it's necessary to apologise for children not being silent for a couple of hour flight.
Would you just always apologise because you have a child with you who's made a noise ?