I heard that if you pay child support you can claim one of your kids??

If the custodial parent gives you a signed Form 8332 you can claim kids. See the form and instructions here   ;  https://www.irs.gov/pub/irs-pdf/f8332.pdf

Paying child support does not mean you can claim the child.  As stated, ONLY if the custodial parent has signed a Form 8332 then you can get the child tax credit.  Otherwise, only the custodial parent can claim the child.  Child support is not deductible on your tax return.