You can move between children from the app's child selector, and in the entry view you can also swipe between children to log quickly without backing out each time.
Switching in everyday use
Use the child selector when you want to change the active child for the app.
In the entry view, swipe between children when you are logging back-to-back events.
Why this matters
Switching the active child keeps entries, reminders, Insights, and milestones tied to the correct profile.