Teenager

Hi, it depends of what does your son like-- if he likes asian food then there are asian restaurants around brussels. Or watch movie with him expendables. Or visit a museum. Or a kasteel. Or just give him a gift that he likes :-)

Advance happy birthday to him

You have to think teenager and as that the idea of being dragged out for a meal is probably not something that will excite him. Better to take him to somwhere where he can be nearer young people so try something like go-karting, 10 pin bowling or some other activity that other people his age may do. At 16 food in a fancy resteraunt with mum and dad will probably be his nightmare scenario.

WOW! I disagree with Richard. When I was 16 for my birthday my father took me out to dinner. It was a sweet father/ daughter date that I will never forget. I hope my own son will want the same. As restaurants, I have a few ideas:
Elegant (expensive): http://www.truffenoire.com/
Different from what I was used to (eating with your hands): www.little-ethiopia.be/ in Antwerp
Easting Japanese (show-cooking): http://en.resto.be/restaurant/overijse/3090-overijse/21166-tokyo/ in Overijse (a bit expensive, but nice- check Groupon)
Another Japanese in Brussels ( most typically to my Japanese experiences, but is very casual) : http://en.resto.be/restaurant/brussels/1000-brussels-center/35223-anata/

Also, there is Durbuy adventures: check out this site http://www.durbuyadventure.be/en/

Have you thought of an overnight trip somewhere (Amsterdam) or a day trip to Monschau (http://en.wikipedia.org/wiki/Monschau), Brugge , or Durbuy?

If you tell me a bit more, than maybe I have a few more suggestions.

Hi tanby, I've never eaten there but I believe you get a good view from the tip of the atomium. Might need to book.
Also there are some good multiplex cinemas that often have films in English, with French and Nederland titling. Check out cinebel.be
They list all the shows you can search by genre cinema etc. look for. OV. And you can see all the blockbuster out now,
If he likes amusement parks there is one in Wavre not fabulous but maybe an idea https://www.walibi.com is accessible by train I believe. It has at they'd indoor water park so take along swimwear.
Lots of museums check out http://www.365.be/?lang=EN
Trip advisor also has several restaurant reviews as does the bulletin.
Hope you have fun

My son just suggested booking a scuba lesson at nemo33 which is a deep diving scuba training pool. He said you'd need to book.
Does he like walking some great places to see if you get the train to the Ardennes.
Day trip to Paris? Expensive but doable, Amsterdam also is great fora day away.

Saw someone mentioned the Japanese resto in Brussels center called "Anata", can't help to post this as we had a very bad experience at this place -- the service was rude (our next table left with anger too), we have to pay in advance, the food tasted like leftover in fridge for a week, and the dishes were DIRTY -- we would never go back and always recommend people not to go there.

Ps my son says the nemo33 has a cafe can't voucher for the food. Walibi take a coat of its forecast for rain. Most of the question are outside. Book on line to save some money and plan what rides you will go before you arrive, it's all pretty flat and easy to walk round queues can be large if it's hot. Be aware on, food side is mostly junk food in there's owe usually take a picnic they have lockers if you go by train. It's not the best theme park on the planet, but there are some roller coaster and the water park bit is fun. My kids all enjoy it they are 22-14.
If you drive you have to buy a parking token, but you can get a hand stamp and exit to your car for food if you want to. Hope you have a great weekend.