"Cat" and "hat," for two (6)
I believe the answer is:
rhymes
(Other definitions for rhymes that I've seen before include "Nursery . . . . . . are simple poems for children" , "Nursery . . . . . . are jingles for children" , "Nursery . . . . . . are simple ditties for children" , "Similarities of word sounds as in verse" , "Terminal sounds are the same in these" .)