Christmas present for my 4 year old in his space phase. Now his favorite socks for sleeping or around the house (unless he wants to walk - he's too bulky for that). Only inside as they are too bulky for his boots but will fit as the boots grow.
Pros
These socks are very thick and soft, I like the grips on the bottom.
Cons
Socks and slippers may not be suitable for all children in the stated age range.