Here is another single light with a reflector. The strobe has an octagon softbox on it. It is overhead and aimed down at a 45-degree angle aimed at the subject. Just off to the side and a little lower than the subject is my reflector with the white side. The reflector utilizes the light from the softbox and acts as a fill light.
When doing a simple light set up like this, one of the main things I use to gauge quality is the reflection of the light in the eyes. Do not make this the only thing to adjust off and don’t let sticking to it hold you back but it is a good place to start. Those lights tend to help pull the subject in to the photo so if you need to move a light to get a better light in the eyes do that. As to where exactly you want that light, well that is up to you.
Finally, another trick when working with one-year olds is go with what gets them to move. In her case, me singing “the wheels on the bus” got her smiling and doing the round motion with her hands. Sometimes it’s a toy, sometimes it’s a song, but try everything you got to make it happen.