Agree with Brett plus you have the wonderful addition of a father who reads in front of his son- superb role modelling. This is soooo important for your son's future reading that he sees it as an activity that Dad not only does, but also one that Dad enjoys.
I spent 12 years in an all boys Secondary school and would feel so helpless when mothers wanted to get their teenage sons to read and when asked if their husband ever was seen reading in the house far too many would reply that he was too busy. Boys must see reading as a masculine activity and not just something that mum does.
Having said that there are so many books for young children that also cater for the adult reader as well.
A few to include for Dad's reading are:
How do Dinosaurs Say Goodnight? By Jane Yolen
Amazing Machine series by Tony Mitton- Amazing Areoplanes, Dazzling Diggers, Roaring Rockets, Tremendous Tractors- over 8 in the series
My Dad, by Jeanette Rowe
The Daddy Book, by Todd Parr
The Best Father of All, by Peter Horn
(buy the last three books and he'll have to drag himself away from his novel to read them to your son!)
Encourage your partner and remember you are luckier than some that he actually will read anything with your son.