Good guess Kath. Let's just agree that within MB mythos, it is Kermit's sister who is Robin's mom.
Besides, MB was meant to stand on its own apart from the rest of the Muppets cannon anyway. And believe you me, you'd want those Muppet Babies to stand well apart from that cannon, especially should Crazy Harry or Gonzo find it and light the fuse.
However, as for one last bit of mind-messing... Remember the episode titled "The Incredible Shrinking Weirdo"?
Well, there was a scene there with grown-up Kermit in front of the theater's red curtains introducing Gonzo, and then we see Kermit (the real Kermit) talking to a cartoon Baby Gonzo dressed up in tux and trying to stand up on his eggbeater for his act.