give him BBC documentary movies abt... ...science.

planetarium, aquarium, zoo. is he REALLY interested in science or are you trying to get him interested in science?? i mean, he IS only, what, 6? 7?

offer opportunities, but don't push. i had the same issue with both of my kids. imagine my horror when they both spontaneously told me at the dinner table, "I HATE SCIENCE!" try to find fun gee-whiz ooh-ahh activities (rocketry, chemistry, electronics, robotics), but if he is lukewarm, back off and try again in a year or two. Just this year my 12-year old told me she's lovin' science, particularly astronomy. It's an age/phase thing.

a lightsabre teach him to build.

science center/museum. and then get him something he's interested in from the gift shop

Chemistry set.

Send your nephew to science camps? A visit to a science center or similar interesting locations to show your nephew the weird world we live in...and amaze him with science experiments...make him ask more questions :)