If it is anything like when I was a kid, it is hard for the boys to not get kicked out of school due to the other students picking fights with them. It is not like they have access to daycare back then.
Might not be the case with the kids you are seeing, but you never know how they ended up being out there.
The kid across the street from us has been kicked out of three schools I think. I don't know his story, but his parents seem to be immigrants and speak an indigenous central american dialect. They don't seem to give their kids much attention, so sometimes when one of them misses the school bus they knock on our door and ask for a ride.
We have a large migrant community here, it's something like an influx of 60,000 migrants through the Monterey Bay area each year. There are fields all around the area, regularly worked throughout the seasons my mostly immigrant farm workers. The kids I've sometimes seen are definitely working alongside the adults. For all I know their parents aren't even there, and I'm making presumptions. They could have been separated from their parents, or be orphans. Either way, it's sad to see them working the fields alongside adults at 10 years old.