Need some advice for my 16 year old son who wants to bulk up?

My son is around 5'9" and weighs just under 120pd, he is very slight build - like his father and grandfather. but he is wanting to bulk up and i really want to support him but would like it to be by eating a good diet rather than any of the products available. so what type of foods should he eat is there a combination that works best. i thought eggs and meat/chicken would be good but what other things should he eat to help in the digestion and absorption of protein. again i want it to be natural i believe you can get all you need out of our diet. i also thought of milkshakes with eggs in them. he was given this protein shake by a freind but i just dotn want to use powders i want to create them with natural products. i am also stressing the importance of exercise he is doing judo and wants to start weights. is it still important to do cardio? any advice would be good. Tweet