I don't think Trump ever developed a theory of mind when he was a child.
"Theory of Mind" is the developmental change where you realize that other people know things that you don't know, and you know things that other people don't know. It usually shows up before you turn five, kind of concurrent with a solid grasp on language. But I don't think he ever got it.
So he doesn't understand how people could know words that he doesn't know ("groceries"), he doesn't understand how people could understand the importance of things he doesn't understand the importance of (pretty much every government agency), he doesn't see any reason for social supports (because, see, he doesn't need them). And, paired with his obvious narcissism, since he loves himself, he is psychologically unable to conceive of the idea that other people could exist who don't love him.
Under this framework, he can never be wrong, because he literally knows all the things (the hurricane path map). He can never have done anything wrong, because he knows what's best. And he can never have broken any promises, because he knew what would happen and made the choice on purpose.
But he's also been around for long enough to prove all of that untrue, so he's had to carve out little exceptions for himself: specifically, that (1) everyone who doesn't like him isn't really a person, they're actually evil and bad and nobody likes them (because he doesn't); (2) everyone who knows something he doesn't is either keeping secrets or a super-genius, depending on whether he likes that thing or not; and (3) when his actions have negative consequences that actually affect him, it's because of one of those evil not-people plotting against him.
So, anyway, when you call Trump a toddler, you're actually giving him a few extra years of credit that he hasn't earned.
I mean, it depends on whether you mean "can say some words" or "can actually carry on a conversation." The speech thing can vary pretty widely; I've got an 8-year-old who was speaking in complete sentences by, like, 20 months, and an almost-3-year-old who was speech delayed and is really only just grasping the idea of expressing his preferences to us with words. Our other two were in between those two extremes.
You're not wrong, though. In any case, he is not fully-developed as a human adult.