Disciplining other kids at playdates: is that OK?

Have you ever been in charge of your friend's kids, and wanted to pull their hair out after they hit your child? To discipline other kids or not to discipline that is the question for so many parents, who don't quite know how to react in these difficult situations.

My friend and I were sitting in the garden with some nice, cool drinks and one of those inflatable kiddie pools. The kids were having the time of their lives, splashing each other with water and enjoying the sun. Until, that is, the time to leave the pool came around and my friend handed my daughter a purple towel to dry herself off. Her boy, age three, got angry and decided to shove my daughter into the pool... and I watched in amazement (for what must have been little more than a second) as he proceeded to hold my also three year-old, a little smaller, daughter under water.

Mama Bear didn't need to think over her actions, lifted up the boy, and then took her daughter out of the water. My friend stood by silently as her son started to bite my finger. It bled. I'm generally a non-violent parent, but I hit the boy. Then my friend came into action. She told me I was wrong to hit her son, but didn't comment on the fact her son had tried to drown my daughter second earlier.

Needless to say, we're no longer friends. But these kinds of situations are awkward, and perhaps even more so if you are left in charge of your friend's or relative's kids, no other parents present. Is it OK to discipline other peoples' kids? Is it OK to send them to time-out, to yell at them, or even to spank? When someone is in danger, my answer is yes safety always comes first. But obviously, not every parent agrees with this.

The only sane advice is to talk this issue over before a challenging situation comes up. Discuss your parenting philosophy and views on discipline before you are left alone with someone else's kids, and also before you leave your kids with someone else.