Children do have a habit of kicking the seats in front of them, kids are kids. Most parents say "I'm very sorry, I'll try to stop it happening again." and then do something about it. But there are some precious parents out there with equally precious offspring. Either their little darling didn't do it, their lovely little thing is sitting in a paid seat and can do whatver it wants or maybe they just can not stand criticism. Fortunately there are not that many anti-social parents so these things don't happen that often but it's best if such precious people do not travel with others.
With regards to luggage it deoends on local law and airline policy. This family thought they were going to fly. Admittedly, it could have been a set up but the chances of annoying someone enough before flight and then getting deplaned are less than successfully getting a prohibited package in board using other means. Besides 100% bag screening will reduced the chances of getting anything untoward on board to a negligible level. So if their unaccompanied bags flew it was an entirely reasonable thing to do.
And as ever, more facts would be nice. But now lawyers have got involved they will be lost in the action.