Many families cannot afford to take care of their young children without working, nor can they afford to pay someone to do it for them. They need to work, and they need someone else to watch their baby all day for free, otherwise they won’t have enough money to live. Kids don’t spend their childhoods at grandma’s house because their mom thinks that it will be a valuable bonding experience between grandmother and grandchild; kids spend time at grandma’s house because it’s free, and grandma is a trustworthy figure who has the kids’ best interests at heart. 

There’s a big difference between leaving a baby with a trusted adult figure who has raised or cared for children before and leaving them with an inexperienced young family member who can barely take care of themself, let alone be the sole caretaker of an infant. Babysitting for a couple of hours is much different than full-time childcare.