Sadly, I do know of some large breeders who do this.
I put a deposit on a little fellow when he was 7 days old, expecting to not bring him home for months. The breeder called me when Chester was 3 months old and said he was weaned and in the pasture with the other weanlings. I was very upset that he had been weaned so early.
I drove 2 hrs. there to check on him. I was surprised to see him looking fit, and happy with all his little buddies. Apparently, he was a handful for his momma, was eating his food and hers! He had become buddies with another foal that was a bit older and ready to be weaned, so Chester moved with him. They said he whinnied for his momma a few times, then started separating the fillies from the older colts! I made arrangements for him to stay at that farm for another month or two, but a week later was called to come pick him up. All the weanlings had been sold and were leaving by Christmas Eve for their different destinations. He would be all alone!!
To finish the story, I ended up with an unexpected Christmas present for my two gentle mini geldings. They spent the first night just out side his stall, watching him through the openings and touching his face. He had been very afraid of the breeders and other people. I put him in with my boys the next day and crossed my fingers. It turned out great. They have raised him and taught him manners and that humans are wonderful slaves.
In this case, it worked out. I really think it is important that the foal stay with it's mother much longer than 3 months. They learn so many things from them besides just getting milk.