Wetness indicators on diapers are helpful in determining when a baby or toddler is wet enough to need a diaper change but they're not really needed and parents have gotten by for years without having a wetness indicator on the diapers.
You can easily feel a baby or toddlers diaper to see if it's swollen up and squishy and needs a change.
A newborn goes through a lot of diapers per day so you'll be changing a newborn baby up to 10 to 14 times per day.
For a toddler they tend to wet their diapers less and need less diaper changes but you should be checking the toddlers diaper every 2 hours to see if it needs changed.
If the diaper can be squeezed in your hand and is squishy then it's likely time to change the toddlers diaper.
If it's been 3 hours since the toddlers last diaper change then the diaper is likely ready to be changed and wet enough to warrant a change.
Even if the diaper isn't fully saturated a diaper should be changed after 3 hours since the urine can turn to ammonia and give your toddler or baby a bad diaper rash.
For poop you can easily tell by the smell and it should be changed immediately.