I think the statement:
"Jesus saw some babies nursing. He said to his
disciples, 'These nursing babies are like those who enter the kingdom.' "
Is probably more curious to the ear of the modern listener than it was to the ear of the listener 2 centuries ago.  Drawing attention to "nursing babies" would be no different from "wet water" or anything else that is perfectly ordinary.  The often quoted statement "out of the mouths of babes and sucklings" (Psalm 8:2) is in the same context - there were no other types of babes, and the sucklings were probably up to 5 or 6 years old. 
I found the Gnostic Gospels pretty rambly and it's not surprising that someone hid them away.
... for what it's worth.

Joy Johnston, FACM IBCLC
Midwife and Lactation Consultant
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www.webrider.net.au/~aitex/joy.htm