This suggests quite sophisticated social modelling by the babies IMHO, as it implies they could put themselves in the small circular shoes of the creature in the cartoon, understanding that it 'wanted' to climb the hill, appreciating the concepts of social interaction and friendly assistance, and managing to extrapolate a general personality characteristic from an example (the triangle behaved in a friendly way, so I like it more). This is very interesting to me.
It also reinforces my belief that community, reciprocity and altruism are part of what makes us human, not social add-ons. I think we are expected to suppress these sentiments, and that causes a lot of pain.