Eggmus: What's the line between pretending and mimicking?

Epsilon loves vehicles, especially the broken cement truck that lives in the sand pit at the playground. He also loves his stuffed dog.

At the playground, the broken cement truck and his toy dog often go on slides, or in swings, or in rides in other vehicles at the playground. He shares his food with them. He puts them to bed.

Okay, so this isn't terribly surprising behavior for a toddler, though I haven't seen a lot of other toddlers putting trucks in swings, but I have a small N.

But it has me thinking, where is the line between pretending and passing on behavior we do to him to objects he likes. We feed him, we put him to sleep. Sometimes, he tries to put us to sleep, or feed us, or push me when I'm in the swing.

For instance, in the area of language acquisition, the current thought is that Epsilon is absorbing grammar as well a vocabulary, and practicing a new skill, not just mimicking the words and sentences we say to him.

What's going on in his brain now? Is he exploring social relations by sharing with his toys? Is he simply copying the things we do to show him we care about him? Is there some other skill acquisition going on?

This is where I really wish I had a degree in child development. And also that I knew what part of a cement truck's engine craves broccoli.