What happens after a motion for default has been issued on behalf of myself for a petition to determine paternity and my child's mother didn't respond until after the 20 day period?
Actually, nothing. Clerk issued defaults are useless in actions involving children. She will be able to raise issues at trial/hearing that pertain to the child/children.
Nothing. The court prefers to resolve matters on the merits.
A default in a family law case is meaningless.