This type of DIY project is my favorite: low cost, low time commitment, and high impact in a kid's room. I felt like Liam needed some "kid" elements in his room to make it feel less formal and decorated, and this is a good start.
Small hole punch or awl
Cut your leather (or vinyl) into long strips that are at least 5" wide. Place two strips wrong sides together (so that the leather faces the outside). If you're using real leather and concerned about your sewing machine, pick up a set of leather needles. With the vinyl I used, it was lightweight enough to be no problem at all.
Remember drawing stars in elementary school? That's exactly what you're going to do with your sewing machine. They do not have to be perfect. In fact, it looks way more fun if they're not! If you're nervous about sewing without a line to follow, use a knitting needle or a mechanical pencil without the lead to trace out your lines before sewing them. If not, just go for it! You want to make sure you're sewing the two layers together as you sew the shape of a star. Repeat this for at least 8-10 stars.
Once you've sewn several stars on a strip, cut them out with your scissors, leaving a small edge around them. Then with a tiny hole punch (or an awl or ice pick), make a hole in the top of each star.
I used cotton string to thread through the hole, tie it off, and cut off the end. Repeat for each star. Make sure to leave several feet of thread (up to 5 feet) on each star so that you can play around with the different lengths once you choose a place to hang them. Finally, using a small piece of scotch tape, tape them to the ceiling at different heights over your baby's crib, your child's bed, or over a play area. Trim off the ends of the string and you're done!