There is a debate about tibetan tradition of picking a one or two years old child to become a life long monk. Some people talk of human rights of the child being bafoués. But I have seen children nuns and monks who were delighted to be in the nunneries or monasteries. So I know some children can thrive as young sangha. 

The example that brought this to my attention was the 4th Jamgon Kungtrul born in 1995 in tibet who disrobed at the age of twenty and disappeared from Indian circles of tibetan monks. He said his upbringing had been tyrannical and awful. And he felt like a burden as the 4th. He left to pursue his life long dream of being a doctor but no successes were heard of for him on the front. Leaving the robes without any money would be very hard. And no real education except the scriptures.