Not many details, sorry!
An old film, at least early 80s. A boy aged 10 and girl aged 14, following a nuclear war or something. The young girl had a baby, and the film followed the baby as if grew up. Due to the nuclear event not many people were around so the baby grew wild and communicated by grunts etc.
Disclaimer: friend who is relaying this has a bit of a wild memory for detail, so parts may or may not be true 