Seems unlikely, given that the romance in Monsters Inc (such as it was) was a mixed-race one. I think it's just that Pixar films don't tend to have a big romance episode - if you think about Toy Story II, for instance, there was no overt sexual/romantic element at all in the relationship between Woody and Jessie.

I suspect it's more that the filmmakers believe (probabaly correctly) that kids understand friendship better than romance/sexual attraction, and find the former easier to relate to. Both B and C certainly seem to react to kissing scenes in much the same way as the kid in The Princess Bride.