I didn't see much of it but from what I've seen and read everyone seemed to be displaying perfectly normal behaviour.
Child gets taken to an important but boring event, child acts up as is normal, parent deals with it, end of story.
I think the kids should have been there, it's an important family event and all of us as children had to suffer through several of them and we were expected to behave, when we didn't we got told off. Exactly what happened in this situation. Kids need to learn from a young age how to behave and whilst it's expected for a 4 year old to kick up a fuss they should be reprimanded if they are being cheeky/naughty because that's how they learn right from wrong.
I feel like parents, especially royal ones can't win. Had Louis been left at home there would have been people criticising that saying he should have been there, taken away by a nanny would have been about Kate not parenting, sat there like an angel it would be why is he so robotic, Kate shouting at him would have meant she was a bad parent, ignoring it likewise.
Everybody judges, including me but I think sometimes people just need to keep them to themselves. Kids are hard work, some more than others and we just do the best we can.