Of course I had to make some felt shorts to complete the birthday outfit. See felt crown DIY here. These shorts are adorable. I only wish I had made matching suspenders.

Use an existing pair of shorts or pants as a guide for the pattern (I probably shouldn't have used grey shorts here - I can see how this is could be confusing). Fold them in half and trace them onto some wax paper (I used newsprint here but I don’t recommend it because it can rub off on your fabric).
Cut two small holes into the inside of the waist hem. Use a safety pin to thread some elastic through. Sew or tie the elastic together.
One thing I learned on this one is to add a bit more fabric to the bum-side (especially when your little one is still in a diaper).