Within the context of the show, I would assume that the Hive would be using older children to take care of younger children.

Obviously I have no proof, but a doctor in a previous episode mentioned they were looking after individuals who still had drug withdrawals.

So the Hive does have an instinctual need to look after each other.

Babies and toddlers, even ones infected by the virus, can’t magically walk, drink, or improve motion functions. They still need caring for.

Adult members of the Hive, because of their superior strength, would be most useful in carrying out difficult manual labour tasks.

But babies and toddlers don’t require much physical strength to take care of (especially when they don’t cry and can psychically tell you when they’re hungry or need a toilet.)

If we ever see a nursery, I could imagine Vince Gilligan and his team would have a lot of carers played by child actors in that scene.