These can be pulled on over your head like an oversized T-shirt and each have three baby-sized pockets, with reinforced seams, that can each hold 20 pounds. Assuming the adult wearer is strong enough, the vests and aprons allow them to evacuate three babies.
Importantly, the pocket arrangement allows the wearer to retain the use of their hands. When descending a staircase during a fire, for instance, you'll want to be able to grab the handrails securely when bearing the extra weight. The wearer is also able to open doors or use a phone, without having to worry about dropping a child. Additionally, they could use both hands to lead older children, meaning one adult could conceivably evacuate five children total.
Lastly, the pockets are placed such that the wearer can sit without putting the babies in harm's way.
This is one of those objects you'd hope you never have to use, but if you did, would be well grateful it was designed.