Children are the big thing right now (and probably for as long as our society stands) that you have to be careful about. You will hear plenty of stories of parents who have taken pictures of their kids in their birthday suits cause they were being cute and jumping on the bed, and how when they got the film developed they were reported. Go to pick up your pictures and you are arrested and spend thousands defending yourself legally. Plenty of lives have been ruined by this.
I think as long as you use good judgement, nothing is off limits. I'd ask before taking any pictures that could be crossing the line - as mentioned pictures at a funeral. I would definitely ask before taking any pictures there simply out of respect to the family. As for childrens sports, I'd probably go to the bleachers and ask if anyone had a problem with me doing it. Anyone who has a problem, ask what number their kid is so you can be sure to avoid him/her. It's just one of those things, you dont want to end up with pictures of someones kid and angry parents thinking you are a pervert. Sad that our world has come to this.