The biggest mistake the majority of daycares do is putting the same ages together instead of having mixed aged groups. In a home setting that is the natural state of affairs (with the exception of large multiples, but those children have a genetic link with each other). Because the children are the same age the developmental quirks to deal with are multiplied. Instead of having only one or two child with the "if I see it, it is mine" (ego-centric) moments, the worker has 8 to 10 children with it. All. day. long.
With mixed age groupings, the older children model maturer behaviour (for their age) and can 'scaffold' the younger ones. Scaffolding is what a Soviet developmentalist named Lev Vygotsky labeled the teaching that happens when children teach each other informally. The younger child has some rudimentary skills and sees the older child doing something that builds onto that basic skill set and tries it. That is scaffolding, building onto what is known. It doesn't happen very much with same-age children. Since children's brain development is experiential (experiences create more & stronger neuro connections), the experiences an older child could offer are not happening that muchin same age groups.