Toddlers stay in size 4 diapers from around the ages of 12 months to 18 months to as long as 2 years to 30 months of age.
Some toddlers may even wear a size 4 diaper until 3 years old or sometimes longer depending on their growth rate, weight and build.
Many toddlers stay in a size 4 diaper for at least a year or longer, although some may only stay in a size 4 diaper for 6 to 8 months before moving to a size 5.
And many toddlers stay in size 4 diapers until they are fully potty trained.
Toddlers in size 4 diapers often go through 5 diapers to 7 diapers per day.
Size 4 diapers are for ages 18 months old to as old as 36 months or 3 years.
However the actual age that a toddler or child would wear size 4 diapers also depends on the child's build and their weight.
Size 4 diapers though are designed to fit children and toddlers weighing between 22 lbs to 37 lbs.
But weight alone cannot always determine the fit of the diaper or how long the toddler or kid will stay in the diaper size.
Some 2 year old's may need a size 5 diaper and some may even fit into a size 3 diaper in some cases.
And then some 2 and 3 year old's may need a size 5 diaper depending on how they are built.
Size 4 diapers are often worn during a toddlers active phase when they are moving, walking and even sometimes even beginning potty training.
Some toddlers stay in a size 4 diaper until they are potty trained at or before 3 years old and some toddlers may need to move up to a size 5 diaper before age 3 and stay in a size 5 diaper until age 3 or a bit over until they are potty trained.
Most toddlers and kids finish their diapering in a size 4 or 5 at most before they are potty trained.
Size 6 diapers are still needed by some kids and even size 7 diapers, but size 6 or size 7 diapers are the least needed diaper sizes.
Also diapers can also fit different even if they are listed as being the same size as some brans of diapers run smaller than others and some brands of diapers run larger than others in the same size.
If the diapers are leaking constantly, leaving red marks on the child's waist or thighs, or if the diapers fastening tabs can't reach the center of the diaper any longer, then it's time to move to a larger size diaper.
Size 4 diapers are often used for a long period of time and sometimes children stay in a size 4 diaper from 12 months to 18 months or longer, depending on your child's growth rate.
And some kids might need a slightly bigger diaper to hold more pee, if they are a heavy wetter, even if the size 4 diaper is fitting them properly.
Larger size diapers have more absorbent material and can hold more pee, but you also need to make sure that the diaper is not too big as any gaps in the legs or too much sagging can lead to leaks of pee and poop.