Based off this big bow tutorial, I made several modifications to create a toddler bowtie.
Cut a 10 x 10 inch piece of fabric. I had a very lightweight cotton.
Roll it up like so, and then close it. Sew along that edge.
The seam is adjusted to the middle
Fold in half and sew again along the short edge
Again, the seam is moved to the middle and the wrinkles are pressed flat
A small piece of fabric (mine was 2 x 2) is folded in half and sewed along the long edge. That seam is then moved to the middle as well.
Wrap it around the middle of the tie to see how tight you think it needs to be. Take it off and sew it closed in that spot, so you make a small loop.
After sewing the middle piece closed, squeeze it back into place in the middle of the tie. It should be fairly tight.
I found that the easiest way to attach it was a simple pin right next to the top button hole