Your boyfriend needs to speak with his probation/parole agent and discuss this situation with them first so that he does not violate his probation. Probation for sex offense charges generally prohibit the person from being around minor children, except for their own children if they were not the subjects of the criminal charges. If he can explain that he has a child on the way with you, and that you two plan to marry, then probation may make an exception to his probation conditions and allow him contact with the children.