Number one, if you have more than one child, make a strong will.
I think that a deep picture frame will look nice. I made one by putting 3 differing sizes of frames inside each other and gluing them securely. Then I painted it to show off the sparklies. The backing I covered with padding (polyester batting) and then satin from some pretty, colored satin. Then I could use a curved needle to get under the jewelry with thread and secure them on it. One of my daughters still has this among her pictures on display.
If the jewelry has a hook on the back of it, that will help a lot. Fine invisible thread will work to stabilize it. You can make this as large or as small as you want. A very small one will look sharp when located in the middle of a big frame. Check out pictures on the Internet to see what catches your fancy.