Ironically, very small children display "sociopathic" tendencies. Toddlers have a hard time empathizing with others just because their brains haven't developed to that point yet - they're very egotistical and all-about-me. They're concerned with getting what they want, RIGHT NOW NOW NOW! at all costs.
It's mostly through contact with peers that they learn how to empathize; if they hit their friend Susie because she took their toy and Susie starts to cry, their little brains start thinking "Oh gee, Susie is crying because I hit her, it's bad to hit even though she took my toy." The toy becomes less important than making sure their friend doesn't feel bad. But again this is a learned behavior and also needs to be modeled by parents so the kids get a consistent reinforcement of that message. (TV and kids' media is not effective at this).
Some kids don't get that modeling from their parents and therefore have less capability for empathy - the oldest Martin child is a good example of this, he clearly takes pleasure in tormenting his siblings because that's what he sees his parents do and he is rewarded for doing so by getting toys and electronics from the YouTube money.
If the stories about Michael's childhood are to be believed, he got the opposite modeling from his mom. He never progressed beyond a toddler's capability for empathy. A traumatizing childhood is also a good explanation for his ridiculous fixation on toys (funko pop), YouTube, and video games - he never grew and matured enough to leave childhood behind, and might be trying subconsciously live a happier one. He's not a sociopath; there is not a brain abnormality that is making him incapable of empathizing at all. He is just a giant toddler.