When we bought my son a Christmas outfit, The shirt fit great but pants waist was too big and the the vest was too big. So I fixed it.
I took in his pant. See my tutorial on taking in pants here
Then his vest was too big so I decided I would make a clip for the back.
You will need a clip. You can buy badge clips, like mine, or you can use another clip. Maybe one you already have around.
You will also need ribbon. My length is 7 inches
Note: After completing my clips I would have liked it to be about 1 -2 inches shorter.
Open your clip and place the ribbon inside.
Then, with a hot glue gun, put some glue on the top and pull the ribbon and press it onto the glue. Do the other side the same way.
You may need to glue the ribbon inside the mouth of the clip if it did not already glue itself while gluing the ribbon on top.
My clips are being reused so they have glue on them
Then your finished, just clip the clips on the vest and ta-da.
All finished and you didn't even have to sew. Gotta love hot glue guns..