This may be why it is best for Cthulhu to never appear on screen. It is going to be very hard to have him not appear as something from a kids show.
Cthulhu did appear onscreen in the Real Ghostbusters
episode "The Collect Call of Cathulhu" [sic]. Which was nominally a kids' show, but wasn't really.
I think they kept slimer out of that, and gave the great one four arms IIRC.