Based on the knowledge I have the only law for a layman in Buddhism is that no child can be ordained without the permission of the parents. However, something I see in this society (especially in rural areas) is that children are handed over to the temples to be ordained (mostly based on something to with their horoscopes) even when the children protest. Am I wrong to say this but doesn't a child's consent matter as well? You cannot be forced to be ordained.
I live in Asia and i am aware of the situation. Yes it is sad and here is how and why it is happening.
The horoscope matter happens because South Asian ideology is dominated by "Astrology". Most of South Asians choose almost everything based on it, child's name,who they are going to marry,their future & etc. Specially Indians are very obsessed in this whole Astrology thing.
So what actually happens?
There is a Bad Habit among some people, they dump unwanted Cats & Dogs near temples. Sadly some children got so called "Bad horoscopes" with predictions like This child is a lethal danger to the father or mother or something like that.
As some people are obsessed with this so called "scientific practice" they tend to go to extremes. You would be surprised to know people walk away from marriages & relationships based on these predictions too.
So now the "Puppy situation" comes into play. They take children to temples and make them become monks. The temple has no choice here because the temple can't send someone away when the situation is like that.
There is another side to this....
Some parents can't take care of their children. So they would take boys to the temple to become monks. As the temple take care of their education and every other need.The parents are happy that their children are going to have what they would not have if they stay home.
Knowing that some children would not stay in monkhood after they are old enough, the temple still to all that needs to be done for them. There is no bind keeping them from going back. Temples finance the learning of these new monks until they get a "Bachelor's degree".
This may be a situation in which a child's views or hopes are neglected, But if it wasn't for the temple who knows what will happen to these children?
In my own country we had some terrible incidents, some single parents killing their own children and killing themselves. These events occurred in a short period of time and all these incidents happened because of either Family or Financial trouble.
The Temples provide a roof over these children and give them education. Temples do not hold these children against their will and do not force monkhood. If the children wish to stay without being a monk that is allowed too.
It is as fair as forcing the kids to go to schools, when they refuse. There's usually a probation period as a novice within which they have to prove themselves worthy of monkhood. Even if the parents made the decision based on a horoscope, proper monasteries don't just accept any child unless they see potential for spiritual growth and the Vinaya requirements are met.