can i sue my ex-wife for cleaning out my bank account?

Sue her for what? You must have set up a joint account with her, and there are no restrictions on the amounts either party in a joint account, can withdraw from that account. If you wanted her to have money for childcare, your best bet would have been to set up a separate account for her, close the joint account and set up a new account for yourself, then transfer a set amount into her account each month. But, hindsight is a wonderful thing. At the moment, there's nothing you can do about the money. She hasn't done anything illegal.
If you have the kids, I'm assuming you went to court and got legal custody. It would be very unusual for a wife to pay child support to a father, unless you are a stay at home dad, and she's some kind of highly paid professional.

If her name was on the account it's doubtful you can do anything about retrieving the money. Go for child support payments.

You should consult a lawyer. For a few hundred he can tell you if you have a case or not. Bring your divorce papers. It's mostly going to depend on what the divorce papers say.

You have another problem. If she has no money, then suing her won't do a bit of good.

Child support is a different issue. If you have custody of the kids then you can ask for child support.

you let her clean you out and did not complain for three years? You never cut off her access to the account yet you knew she was taking it out?

You can sue, but there is a statute of limitations issue coming into play real fast. Your chnce of sucess is slim.