That would be child support and the laws say men should pay for their kids that they helped conceive. While I agree a more equitable situation would be to allow them out of it since we have abortion on demand, but in a libertarian moral society people be under consensual agreement on outcomes prior to.
Technically men also know that sperm meeting eggs create babies so if they don't want their child aborted they should pick better women to put their dick into.
That's called choice and responsibility.