At toddler group yesterday and they were all 'on form', pushing each other etc. They are all between 2 and 3 and at similar stages of development. My friend and I saw a girl push my DS and he pushed her back, ensuing a pushing battle between them. I took DS away and told him it is naughty to push others and we don't do it. My friend then said that she is teaching her DD to hit others back if they hit her first. Her DD has only just turned 2 so she is younger than quite a few of the toddlers there who are nearing 3.
She did say its probably too young to do it, but carried on telling her DD anyway. I did point out that I would tell this to DS when he was older and at school, but at this age I think they are a bit young to be taught that, especially with loads of toddlers all going through the hitting/pushing stages at the moment. I just said I preferred to tell him it was wrong to hit.