You don't have to change a wet diaper every time the baby or toddler wets their diaper otherwise you'd get nothing done but changing diapers.
You should check a diaper every 1 hour for younger babies and for toddlers you can go as long as 2 or 3 hours in between checking their diaper for wetness and needing changed.
It's okay if the diaper is just a little wet as diapers today can absorb a lot of urine and the wetness is held away from your baby or toddlers skin.
Once the diaper is really squishy then it's time for a diaper change. If they poop in the diaper then you should change the poop diaper as soon as you notice it.