If he evolves it into a Snorlax, he'll get Snorlax babies.
I'm not sure what the problem is though, sorry. But don't evolve it.
When you evolve it into a Snorlax, give it Lax Incense to hold. That way you can get Munchlax from the eggs. But I am 99% sure that you cannot make eggs using a baby Pokemon as one of the parent.