We need to show our politeness and respects using the ending 요, 하세요, 드려요 to somebody who is older than us. The main topic is 생일 축하 (Happy Birthday).
But we dont say that to our parents or grandparents and boss like, “Mom, 생일 축하!”
there is no sense of expression in there at all!
So when you talk to elders, make sure you use the polite way.