Playgroup is for toddlers from 18mths old onwards, usaully 2 hours.
PreNursery = 3 yo (3-4 hours)
Nursery = 4yo (3-4hrs)
Kindergarten = 5 to 6yo (3-4hrs)
Childcare depends whetehr you want half or full day. From 18 month to 6yo. Childcare usually is for children whose parents have to work and no one can tc of them. Other than taking care of them, the teachers will also give them lessons just like the usual preschool (also PG, PN, Nursery, Kindergarten). Only difference is, the kids spend longer time in Childcare, shower and nap in sch.
Hope that helps and please correct me if I am wrong =)