A.F.
Hi S.! You are so thoughtfull! My first thought was a gift certificate for a restaurant so they could have a date night.
Also, have you seen the new daddy tool belts? I've seen them online and they are kind of cute. They have "supplies" for Daddy's doing diaper changes like tongs for changing diapers, goggles, ear plugs and a mask for the smell. You could make your own instead of ordering. You can see examples at www.babydepot.com
Also, if they are coffee drinkers you could get them a pound of nice beans and a couple of mugs. Some caffine to help dad after those sleepless nights:)