From the Super Mario Wiki
Baby Cheeps, or baby Cheep-Cheeps, are small Cheep Cheeps that Big Berthas take care of in Super Mario Bros. 3. Big Berthas periodically spit their babies out and put them back in their mouth. In case Mario (or Luigi) defeats the baby (with a fireball, for example), Big Bertha will continue to "swallow" the area the baby used to be, and will spit out a new one later, as if the original had never gone.
What seem to be three baby Cheep-Cheeps appear in the The Adventures of Super Mario Bros. 3 episode "Reptiles in the Rose Garden". A single baby Cheep-Cheep appears in the Nintendo Comics System comic Love Flounders as the child of the smitten Bertha.