It takes the same amount of time for a kid to digest food as it does for an adult or toddler to digest food.
For most people it takes between 4 to 8 hours to fully digest food they've eaten and to poop it out.
For me I usually need to have a bowel movement 4 hours after eating but sometimes the bowel movement doesn't happen until 8 hours later.
It all depends on how much fiber you've eaten as more fiber based foods cause you to poop more often and more than eating non fiber based foods.
But the kid should be ready to poop within 4 to 8 hours but the kid may not even poop until a day or so later and that's normal too.
There's no set amount of times that a person poops though and everyone is different.