From the Super Mario Wiki
Baby Cheeps are small Cheep-Cheeps that Big Berthas take care of in Super Mario Bros. 3. Big Berthas occasionally spit them out and swallow them. 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 been defeated.
Three Baby Cheeps appear in the The Adventures of Super Mario Bros. 3 episode "Reptiles in the Rose Garden". A single Baby Cheep appears in the Nintendo Comics System comic Love Flounders as the child of The Big Bertha who falls in love with Mario.