At their young age, it typically takes children the ritual of performing arithmetic algorithms at least several dozens of times if not a hundred times to get them to understand and internalize the algorithm itself. You can't actually teach the algorithm itself because they haven't studied basic algebra yet, so the only approximation is using the algorithm on multiple numbers. Then afterwards just give them a calculator.

In contrast, in high school, when a student has sufficient mental maturity to understand algorithms abstractly, it suffices to have the student do a few integrations by hand (say using the integration by parts technique) and then hand them a computer algebra system.