^ No, SpongeBob has innuendo. Subliminal messages are like the infamous "SEX" letters embedded in the dust when Simba flops down to the ground on the early versions The Lion King, or the penis seen in the towers of the Atlantean city on the early VHS covers of The Little Mermaid or the priest with a supposed erection on the early versions of The Little Mermaid. I know one that still is around is when the voice actor for Aladdin says "Good little teenagers. Take off your clothes." It can still be heard even in TV airings of the movie.
I don't think there were any subliminal messages in The Land Before Time and its sequels. Universal was so hellbent on making them as child-friendly as possible that they probably went in and checked to see if there were any hidden in the animation. That and the animators and artists at Universal Animation Studios probably weren't like that.