They go through stages in which their body form changes radically, whereas human infants have approximately the same form that they will have as human adults.
(They; go; through stages) (human infants; have; approximately the same form that they will have as human adults) (approximately the same form; will have; as human adults)
They human infants approximately the same form
go have will have
through stages
approximately the same form that they will have as human adults
as human adults