OK...here weeeeee go!! I might hate myself for bringing this up....BUT, maybe she drowned in the tub.
I'm NOT gonna go with the "sexual abuse" combined with the "drowning" thing, so don't worry, for anyone having the shakes and flashbacks from being submitted to those two words combined in one sentence last summer.
IMO, that's pretty late for kids after a baseball game...especially a 6 yo....just IMO. Have NO first hand experience...but I used to watch kids games with a friend, and it wasn't THAT late. IMO.
At any rate, if I tried to GUESS, I'm thinking a neighbor or relative notified CPS of some sort of "neglect"...or what THEY thought could be classified as that.
SC mentioned Isa said she was "tired"....MAYBE, she needed a bath, or they said she needed one. Maybe SC was supposed to be "watching" her or at least check up on her....help her out of the tub, etc.
HE said he was "watching" the baseball game and "fell asleep"....IIRC.
When he woke, he FINALLY remembered Isa....or even forgot and went to sleep.
She COULD have tried to get out of the tub herself...slipped and klunked her head...OR she COULD have fallen asleep in the tub and drowned.
Whatever it was, as we know, there's usually some "grains of truth" in peoples stories.
IMO, I believe the next door neighbor about the 6:30 voices...that could be when SC remembers Isa's in the tub, and finds her dead. Yada, yada....we know the drill....set up/make up a story about the nanny....OOOPSSS, I mean an "abductor" taking Isa.
We know CPS had been called earlier, people get scared and don't think anyone would believe it was an "accident"(oh, boy...pool/tub...potato potahto). OR, how BAD it would make SC seem....can't have THAT happen, since it seems, IMO, he'd be REALLY mortified by it in front of the community. (oy!!)
Or, that the other boys would be taken away, as well.
ETA: As far as falling asleep in the tub, I did it when I was in my teens...BUT, I was tall enough so my head didn't go under. But, weird feeling waking up in a tub full of H2O.