Walk through a few times to learn the layout. Brands will be placed in certain areas, the division between NB-18 mos will likely be separate from 12 mos-5T even in the same brand.
Learn where to find the sewn in dpci tag on each clothing type, or if a particular brand even has one.
I haven't worked in a few months, but see if socks, undershirts, and underwear are still in baby hardlines, guests would search for those in NIT and needed redirected.
Clearance will be a nightmare and will need frequent upkeep.
A lot of boys folded pants and girls folded pants seem the same but have subtle waistline differences. Learn those.
Watch for lost kids and make sure alone kids aren't lost. Little kids play hide and seek, it's what they do, and the racks make it easy for parent to go one way and kid the other. And some kids are like some adults and don't want to be a bother, so they won't say they are lost unless you ask them.
Watch for patterns in type and cut and color. When it comes time to replacing a piece of clothing taken from a mannequin or covering a bare spot in the racks, recognizing the style to blend in will make life much simpler.
Get a lesson on how to take apart and reassemble a mannequin. Nothing like not knowing how to get a clothing arm past the splayed hand while a guest is waiting. Also, guests will offer to help. Don't accept. They could break the mannequin, and if they get hurt helping you, there's liability.