It's actually "babu", which is the Japanese equivalent of "goo goo"--that is, typical infant babble.
Tataran
6 years oldA ghost apprentice that can't scare anyoneParu-tan
9 years oldParu paruI'm jealous.The sound of her crying can break anything.Letty-san
8 years oldWrigglun
3 years oldBody mass is her enemy?SkitterSkitterCrackDai-chan
5 years oldJealousy maskCirno's friend, but no one knows her name.Sanae-tan
9 years oldCOCKROACH
Gokiburi is Japanese for cockroach, often shortened to a capital Romanji GFlan-chan
1 year oldGoo-goo...Re-Reimu's rival, she does as she pleases.Really likes big sister Reimi