I want to give you as full an answer as I can. My background is that I used to be a school teacher, I have 3 young children who have 5 cousins, and I teach a 5 to 8 year old room at church. My wife is a pre-k specialist and I learn a lot from her too.
Please remember that when 4 year old's hit it is not the same as older kids. Generally it isn't bullying either (but it can be), it is simply a young kid who is frustrated he isn't getting his way and he can't find a way to express it. This must be a teachable moment, which is why I am against hitting back and against legal action.
You asked four questions, here are my responses to them.
What do I tell my kids when they get hit?
The first thing I do is ask questions. I can't tell them anything until I know more about the situation. I try to ask questions like:
1) Why did s/he hit you?
2) What did you do before the hit?
3) What did you do after the hit?
4) What is so and so like normally?
5) What did the teacher do?
- sidenote Kids will begin to fabricate certain parts of stories to gain sympathy (4 is a little young for this technique, but it happens), but also they many times don't remember all the details and can fill stuff in with their imagination. It isn't evil or anything, they are kids. I stay on the details like a hawk to keep them honest and get the right information (gently though).
After learning what I can I frame my response to what I learned. I already described the 99% common case above. I explain how it was wrong for the other kid to hit. I tell my kids to be firm in telling other kids not to hit them. Then I tell them to go to the teacher if it doesn't stop. Yes, they are to accept the first hit 1 or 2 times - I believe in patience. However, if the behavior continues and my kid keeps bringing it up at that point I tell her (i have all girls) that she needs to tell the teacher right away.
How have my kids experience this situation?
My kids have been hit at various places. Each kid is DIFFERENT! My oldest is cool as ice and even at 3 and 4 I remember her simply not caring about kids who hit her. She learned very easily to walk away from those kids. The problem ended when she learned to avoid them.
Kid 2 got angry and would hit back. We had to first teach her how to handle her anger at being hit (which I now know was anger at being rejected). We told her she couldn't hit back, this frustrated her. Also, she seeks approval of others, so being hit hurts her feelings, and she won't walk away cause she wants the other kid to be her friend. This caused us to have sincere talks with her about who she hangs out with and who is her friend. It was a good lesson to teach that even people you like can make bad choices. When that happens you walk away and wait for them to stop.
Kid 3 would go hide somewhere or cry. She never fought back or told the teacher. Many times we found out later on accident that she was very sad about being treated mean. For her we focused on self-esteem, facing problems, and told her to go to the teacher.
As a sunday school teacher we have a couple kids who hit others when they are very frustrated. I take them aside, explain how it is not okay to do this. Most of the time there isn't a punishment, but rather a request for forgiveness and we teach the other kid to accept the apology. These kids are friends and they are being trained on how to act as adults. I would not do the same thing for a 15 year old or 20 year old.
There is 1 case where a kid just cannot keep his emotions in check. We know this and we watch for and jump into a situation before hitting happens. It is A LOT of work, but much talking, reassuring, and relationship skill building is taught and practiced. The kid being hit and the hitter both are kids and both need to learn correct behaviors and then practice them.
Fallout with Parents
This is most likely not a big worry. Most parent are aware of their kids behaviors, and even if not they generally know kids to hit sometimes. The biggest threat here is how you approach this problem. First, let the teacher handle it. If you do approach them then do it in a caring way that shows you want their kid to be successful and happy in life and hitting isn't the way to reach that goal. Also, since consequences to 4 year old's hitting are small most parents are not too defensive of their kids at this point.
What would I do
I already spoke of what I would do with the children as a parent and teacher. I will tell you my advice on talking to the teacher.
First, remember if the teacher is young they generally have very limited training and are being paid peanuts. Plus, they have no experience and this may be one of their first times dealing with this. If the teacher is older then you should expect a lot more from her/him.
Second, I would never go to administration or do anything legal unless true physical harm was possible (truly dangerous items in room, or a kid who has major, major, major mental issue or problems that prevent him from understanding or caring about hurting others).
Finally, I would simply bring up the issue with the teacher. Tell her what you learned and what happened. Ask her to keep an eye on the interaction of the hitting kid during the day. After that simply monitor your kids experiences in the room and what the teacher says.
Keep an open dialogue and remember that you and the teacher are a team. It is like marriage in that you and the teacher simply have to get along and find a way to work together. She/he won't be perfect and at times you will find a deadbeat. But, as long as your kids are in that room and school you guys are a team. So I urge you to think in a cooperative manner not a controversial manner.
Good luck with raising kids!