With no free seat, adding a child opens Change plan first.
Every child needs a seat. When every seat on your package is taken, tapping Add child opens Change plan, so you can pick a bigger package before you add them.
Tap Add child on your dashboard. With no free seat, Change plan opens.
Pick a bigger package. Check the preview and tap Confirm change.
Now add them. They take a free full seat on their own. A subject seat you give with Give to… in the Seats list.
