Like a t-shirt quilt, you may end up sewing a few partial seams if you can't figure out a way to piece it together in "chunks". As Prism said, it looks like the pieces to the far right side are pieced together first, then added to the rest of the quilt.
When you decide on a final design, try to draw a square or rectangle easily around as many blocks as possible before having to sew any partial seams.
Don't forget to use a fusible interfacing with those onesies. You are basically making a smaller version of a t-shirt quilt. Each of those blocks need to be stabilized so they are easier to work with.