The weight of a child that size 7 diapers fit is 41 lbs and up.
If your child weighs 41 lbs and up and needs to wear diapers then size 7 diapers would fit them just fine.
My own son who is 8 years old wears size 7 pampers cruisers diapers for bed wetting and they fit him just fine.
But it also depends on the build of the child and how skinny they are.
My 8 year old son weighs 57 lbs and fits just fine in the size 7 diapers.
I'm sure that even when he gets to be 10 to 12 years old he could still fit into the size 7 pampers cruisers diapers.
That is if he needs them for bed wetting.
Size 7 diapers are meant for ages 4 and up but some 4 year olds may be smaller and fit into a size 6 but it just depends on the weight and build of the child.