When should we switch to the next stage child seat?
For a first orientation have a look at the orange ECE label on the back of the child seat on which you will find the weight class or relevant information for that ECE group. In general it is recommended waiting as long as possible before switching to the next stage seat; the weight limits do overlap.
The child's head must always lie within the side bolsters and the back of the head must still be supported by the solid parts of the shell. The head should not protrude the headrest by more than the width of two fingers. With child seats of group I-II-III you may have to adjust the height of the headrest.
Many parents worry about their child's feet hanging out of the infant carrier. As long as the head is well protected between within the headrest, the child is well protected.