My 2 teenagers will turn 18 within 2 years, do I still need to pay child support to their mother under Florida law? Or I can just give the money to my children themselves?

No, you can't give it to them. It goes to the custodial parent (unless your Court papers say otherwise, which I've certainly never seen).

Anything you give the children DIRECT is a gift (in the eyes of the Court). It is in ADDITION to child support.

What do your Court papers say about the age support stops? 18? 21? Some other age?

When support stops is usually stated in your support order. The order will have been issued according to the law. So you need to read the order.

But support is paid to the custodial parent, not direct.

You go by what your court ordered child support paperwork says. And at no time is the money to be paid to the child but to the custodial parent who is named in the child support order.

Agree, the money is not the child's, it is the custodial parents. It is to be given to the parent to offset the cost of housing, of food, transportation and more.