What specifically are you having trouble with bows? At 15 months a "no" followed by "yea!!" when the behavior changed were the most effective tools I had for my kids at that age.

I've been trying to think, time outs started around threeish. Once they were old enough to understand that they were being punished and why. A toddler whacking another kid with a toy is different than a three year old. They have to be able to remember that this behavior is not the right one and make a choice to do the bad one. Does this make sense? I'm having a bad grammar day.