I don't remember very much of toddlerhood.....One incident that springs to mind is the time my cousins opened a gaz bottle that was in the garden, and I ran to tell my parents, screaming about an imminent explosion. My parents took me seriously, I was 2 years old. So obviously I could speak well, and my brain seemed to be in working order.
My mother told me she sometimes had to lock me outside, in the garden, she'd carry me out and lock the door, until I stopped screaming and wandered away to play with ants or something. She says those unstoppable tantrums started around age 2, 2 and a half. I could only calm down if I was alone. Probably early meltdowns.
Other than that, I can remember sitting in the living room on the red carpet, near the window, watching the dust floating in a ray of light. I must have done that a lot, since the memory is very vivid. I remember watching ants carrying things, my mother says I used to speak to the ants, asking them where they were going and why, and followed them around trying to see where they were going. I remember that, inch by inch on my butt, following one ant on the warm concrete in front of the house.
I have no idea if it is a "behaviour". It's just "being a kid", I guess.