The W-4 you give to your employer does not dictate how you file your tax return. It just tells the employer how much tax to withhold from your paycheck. The more allowances you put, the less the employer withholds from your pay. So if you have too little withheld, then you could end up owing--and since you could not claim the children that may have been the case for you.
"....the mothers didn’t let me claim them ..." The custodial parent--the parent the child lives with--is the one who can claim the child on a tax return. IF the custodial parent signed a form 8332 then you could claim the child on your tax return for the personal exemption (which is now gone for 2018 and beyond) and the child tax credit. If the custodial parent did not sign form 8332 then you cannot claim the child(ren).
If you are having too little withheld from your paycheck you can change the W-4 you give to your employer and have more withheld to avoid owing tax next year.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
