The pair will perform a special concert in Reykjavik, Iceland and re-light the Imagine Peace Tower in Lennon's honor.
He explains, "It's too much of an important day to think of my birthday - it's all about being there for mom and remembering dad."
But Sean, who was just five years old when Lennon was killed in 1980, admits he is still heartbroken by the tragedy.
He adds, "I try not to think, 'What if?' But it gets hard for me to imagine what life would have been like if he had lived. I just think it's sad that I've never been able to enjoy an adult relationship (with my dad) like I had with my mom and my friends. But I try not to beat my head against the wall asking what could have been.
"People think I was too young to remember him but there are lots of things I remember about my dad, like him teaching me how to swim, how to use a knife and fork and him rolling up his cigarettes. I remember him telling me about England and promising he'd take me to (his hometown of) Liverpool. But he never did."