Yes, it's a "tock" sound from the rock hitting the shell.
Also, this is just nitpicking, but I'd rather stick to the original slurring, as in some points there's a confusion between chibi-slurring and crying-slurring. For instance, "schut up" would be more baby-like as "chut up" (they can't pronounce the "s") and "chake id eajy" should be "chake itch eajy", as it->id is crying-slurring and it->itch is baby-slurring.
Personally, as long as it's slurred I don't pay much attention about how. Which is good, cause I couldn't hope to keep track of all the ways I slur in my translations ;) I'm sure linguists cringe...
Ah... I'm afraid that I didn't pay too much attention to it either. However, I'll stick to the original slurring as best as I can from now, if it's a bother.