Here's a verse we sang in Primary for its 100th birthday (I was in Primary back then too!). 
It is used instead of the first verse to We welcome you today to Primary. 

Happy Birthday to the Primary,
we sing with love and cheer,
for Primary is going to be,
one hundred twenty firve this year. 

We then just went into.. When Primary first had its start and we repeated the first verse for the ending verse.