What do you think about kids playing online game

Well, depends on how much they play. If they play to much, than you will probably want them to go outside or something.

If they play to little (cuz SOMEONE wont let them) you should let them play. Their kids after all.
some games are good for kids, helps them think outside the box and improves their logic. Just make sure you monitor what they are playing and how long they are playing