Most 2 year old boys and girls wear a size 4 diaper.
But all 2 year old children are not built the same or weigh the same so while some 2 year olds may wear a size 4 diaper some of the 2 year olds may need to wear a size 5 or even size 6 diaper.
But most 2 year olds are wearing a size 2 diaper.
When the child reaches age 3 or 4 they will usually need to wear a size 5 or 6 diaper size and sometimes a size 7 diaper.
If your 2 year old is getting red marks around their thighs or waist then they may need a larger size diaper.
But size 4 to 5 diapers is what most 2 year olds need to wear.