plastic shoeboxes are perfect for hatchlings to about 20g. After that they'll need bigger housing. A plastic sweaterbox is a good size for a juvy/adult.
The plastic boxes? Like sweater boxes on racks? Yeah if you can house an adult in it you can house a baby in it. Obviously would need a heat source and the appropriate furniture for a little gecko versus a big one. If you want to have more smaller individual boxes then you can use shoe box size. 1-2 babies can fit in that size until around 10-20 gram size. Then I think it is better to move them up to sweater box size.
Well, look at the dimensions of the different sizes. A plastic shoebox has about 126 sq inches of floorspace while a plastic sweaterbox has about 238 sq inches of floorspace. Using those dimensions you can find the stackable kritter keepers that are the appropriate size for hatchlings or adults, whatever you need