I am a complete newbie to bonsai. My son gave me a bonsai kit for Mother's Day a couple of years ago.

I have 3 Blue Jacarandas that I have grown from seeds. I have recently repotted them into a 4" pot (from a small 2" pot) and there did not appear to be a main tap root.

The problem is that they are about 2 feet tall now (from the dirt to the top of the plant). I have attached a picture. I am not sure where to go from here. They are kept mainly in the house in a south facing window - with occasional trips outside. We live in Michigan.

Any advice/help would be greatly appreciated.

Hello Jeannie.
Nice to see more people getting into it.
As a few days I responded for a similar case, Jacaranda's are "leggy" by nature, and if you want some proportion on the trunk, it must grow a lot taller than that.
However, in order to grow that much, the tree needs a lot of light (outside), and a big pot so it's roots can grow at the same pace.
Once you get the desire thickness on the trunk, you prune it back down.
What you can do, is to help on the process of ramification, by cutting it's tip top, that will encourage the plant to develop some side branches.

I can't see any pictures. Anyway, I am also growing a blue jacaranda from seed! (although it's from my backyard)
I also took a cutting from the jacaranda tree yesterday because my other cutting died.

Anyway, I have no advice for you.