I know Baby Piggy's voice sounded a little unusual to me, but that might've been because she was voiced by a woman, instead of a man like the adult Miss Piggy is. Makes sense for the young version to be voiced by a woman, to make her sound "younger" I guess.
It seems Frank Welker did a lot of incidental character voices on Muppet Babies, too. I know in my "Scooby-Doo, Where Are You?/Muppet Babies" crossovers, it'd be easy for Frank Welker, since he'd be voicing Fred, Baby Kermit, Baby Skeeter and Baby Beaker in the same series!
I think I remember someone once saying that Kevin Michael Richardson once did a voice on "Muppet Babies."