For a fun and easy idea to use with the song "Called To Serve" get 8 or more envelopes. On the front print the words "Called To Serve".
On 4 strips of paper put the following...
"Congratulations you have been called to serve a mission in...". I did this to two weeks in a row because the children in my ward loved it. The first week I just put random places (Colorado, Japan, Mexico, etc. The second week, I put the name of the places that people in our ward are serving and had the children guess who it was.
On the 4 other strips on paper, print the description of a calling someone holds in your ward and then have the children guess what the calling is and the name of the person in your ward that holds that calling, ie "You have been called to serve and love all of the children in the ward between the ages of 3-12. Who are you??" (answer: the Primary president and her name.) Or "You have been called to love and serve all of the ladies in the ward. You need to make sure that they are loved and that they are visited each month. Who are you??" (answer: the Relief Society president and her name.) I was surprised at how many children in the ward that didn't know who this was!
I put the envelopes on the board and drew names out of a stick jar to have them come up.
I also took a globe with me and had the children that got mission calls find that place on the globe.
Each time we choose an envelope, we would practice part of the song "Called To Serve".
Like I said, the children in my ward really liked doing this and it helped them to see that we can and will serve in the church before and after missions.
Also, if you want to also sing the song "I Hope They Call Me On A Mission" when the children choose the mission calls and "Called To Serve" when they choose the callings, it gives them a break from doing just the one song.