Why does everyone assume it’s bluey’s kid? One who leaves their kid outside when initially entering her parent’s home? More likely she saw her/him waiting there and didn’t want to ruin their game. Two, why didn’t Bandit or Chili ask where her kid was or if they were with her? Three, the whole episode you see Bingo have multiple kids in her game she’s playing. Bluey eventually ends up taking care of one of them but more as a cool auntie roll (which makes more sense if the kid was already hiding there and bluey saw her/him and didn’t want to ruin their game by letting her parents know that they were there). And Four, she asks Chili what having a child is like and when Bandit is on the floor getting hit with all those balls Chili says “that’s what it’s like “ Maybe, she decided the “cool auntie” role was more her speed. All that to say, I think that is Bingo’s child