I have grown two avocado plants from seeds, they are doing well, however, one of them the stem or trunk, just does not seem sturdy. It's very thin or more thin than the other, I cut them both down earlier, like I was supposed to, and the first one seem to grow back, sturdier and thicker, and the other grew back, and keeps getting taller, but doesn't seem very sturdy. I am not sure if I should maybe cut the second one down again to hopefully get a sturdier trunk. Or will it get stronger and thicker overtime, Please help.

I wouldn't be cutting anything off. They need all the energy gathering leaves they have right now.

Avocado trees don't usually branch until they're pretty tall - 6 ft. or more. Cutting the leader doesn't discourage this, they just grow a new leader, also straight up.

Ok… thank u for input… I'll leave them alone… happy new year

Final question on the avocado plant, I am going to replant them in bigger pots, and the beginning it says to leave the avocado seed partially exposed, as you can see in the photo, when I replant them do I cover that up now or do I still leave it exposed.

It doesn't matter now.
The key thing for avos is a deep pot; a very deep pot. Tall and narrow is Ok, but they need depth.

Are they getting plenty if light?

Don't bury the roots any deeper than they are now. The seed will eventually shrivel and fall off so don't consider that part, just keep the roots the same depth.

Yes, plenty of light.. and Thsnk u