Well, let's take this apart. I learned long ago, that if it's not working we go to the next step. Do the opposite is one and making it clear what you're doing is the other. Although that is not 100 percent guaranteed either.
First, if you try not to make a big deal out of it,usually, then he probably knows that. So before you go and do any sideline sitting and to public events you can make it clear what is expected and what the consequences are: i.e. perhaps leaving, not going for the ice cream after, etc.. Do make a big deal out of it (but not in front of all the other perfect moms who give us dirty looks when we are trying to discipline our children. DO THIS At home, before you go.Does he want to be in these classes? If he is doing these things then it might be better to wait a couple of years and not waste money on these things. You yourself won't have fun either. Everyone develops differently and he might not really be a good candidate for these things until he actually desires it himself.Sometimes we get pressured into making our kids iceskaters and they just want to be the one who sells the hotdogs.
Well, I could ramble on but I had one of those clingers and I'd like to say this: I wish I wouldn't have pushed him away all the moments he was clinging because he is in the service now and I don't know where he is or what he is doing and haven't seen him in a very long time. So in this particular case I'd gladly trade one of those seconds of clinging for a moment with my own son. But so be it, if you need to succomb to the pressure that the world puts you, making a man out of a four year old, then so be it.
Is he in school? Pre-school? What do teachers say?
Hitting little brother is not acceptable and perhaps the punishment needs to be again, addressed right away, definite time out or a privelege taken away. I think you are one caring mom and you will conquer this shortly. Good luck!