A baby will wear size 1 diapers from birth until around 4 months of age.
Some babies need newborn size diapers for the first few weeks while other babies may be able to wear size 1 diapers just fine until they are 4 months of age then they will need a size 2 diaper until 8 months of age and then a size 3 diaper until 5 months to 2 years old.
A 1 year olds diaper usually should be changed every 2 to 3 hours depending on how much they pee or if they poop.
A poop diaper should be changed as soon as possible but a pee diaper can wait until a few hours or when the diaper gets full of pee if it's a disposable diaper.
There's no need to change a diaper every time they pee as that is wasteful.
Just check the diaper every hour and change the diaper if it's wet enough.
A baby should not stay in a poopy diaper longer than 10 to 20 minutes if you change the diaper that quickly.
However if you cannot change the diaper right away and your baby has pooped the diaper or your toddler has pooped the diaper then it can wait until you can change it.
For example if you're on a road trip or not somewhere where you can change the poopy diaper right away then you can wait until you can.
I remember taking my babies on road trips and I had 2 in diapers and both of them pooped after we just left a rest area and I had just changed them.
The 5 month old boy was fussy about his diaper but my 2 year old son didn't seem to mind it.
I could not change him until almost an hour later when we finally was able to get off the interstate and find a rest area where I could change their diaper.
Never just pull off on the interstate to change a diaper as it's not worth it.
Just wait until safe to do so.
When a babies diaper is too big the tabs will stretch farther than the middle of the diaper.
The diaper will also slide down and you cannot get the diaper tight enough around your babies waist to hold it up.
A diaper that sags between the legs is also another indicator that the diaper is too big.
Or if the diaper goes more than 2 inches above the belly button then the diaper is likely too big as well.
If a diaper is too small the diaper will fit too tight and the tabs won't reach farther than the sides of the diaper.
If you can't stretch the diaper tabs to at least the middle of the diaper then the diaper is likely too small.
Also you should be able to fit 2 fingers in the waistband of the diaper when it fits correctly and if not the diaper is too tight.
There may also be red marks around your babies or toddlers thighs and around their waist.
If it's a baby old enough to tell you then they may complain that the diaper is uncomfortable.
Some diaper brands run smaller than others even though they list as the same size so you may need to up the diaper size.
Another indicator of the diaper being too small is the diaper leaks often as smaller diapers can't absorb enough pee from a larger baby or toddler so the bigger diaper may be needed.
Tight diapers on your baby or toddler should not cause constipation.
However when the diaper is too tight then it can cause the baby or toddler to become uncomfortable cause rashes and red marks around the child's waist.
Tight diapers can also make it hard for the baby or toddler to move around especially if they are walking it can prevent them from sitting down or bending over easily.
So the diaper should not be too tight anyway and if the diaper fits tight then you may need to change diaper sizes and go up a size larger in diapers.
You should be able to fit 2 fingers easily in the diaper waistband between the diaper and the child's waist.
Your baby or toddler may not be getting enough fluids which can lead to constipation.
Most cases of baby constipation or toddler constipation go away on their own within a week or so but if not you should take the baby or toddler the doctor.