Runner beans - with a wigwam or dwarf runners, dwarf French beans, chilli peppers, potatoes, aubergines, strawberries, salad leaves, rocket - I've grown all of these with varying success but the beans, salad leaves and rocket did best. There are loads more that I am sure others will come up with. Good luck - there's nothing better than eating your own home grown.

I've grown Runner Beans in a large pot with a 3 cane wigwam, Lollo Roso 'cut and come again' Lettuce in a smaller pot as they have shallow roots.

Peas definitely - again with a wigwam, carrots, radishes, spinach beet (you can just keep removing the outer leaves) and spring onions.
I wouldn't recommend potatoes in such small areas as they need a lot of room for each plant.
But why confine him to three containers - if he really wants to have a go at growing veg it would be better in a raised bed or just in the ground. With the carrots pull them when still young and finger sized rather than letting them get large and woody.
Wish him good luck from me anyway. Home grown veg is the best!

If you decide on peas, only grow the 'mange tout' type such as Sugar Snap as you will only get a worthwhile crop in a pot by harvesting them with the pods. Good French beans will go on cropping for months if you keep picking them while very young and give them lots of water and a bit of feed.

i grow beetroot in pots,they dont need any special conditions and theres still time to sow them.
once he has planted one thing he will get the bug.happy harvesting.

in addition to the suggestions try broad beans, lettuce and small cabbages such as grey hound.

If you go to the BBC Dig-in website, you can put your name down for some free veg seeds - I think it's carrots, salad, courgette and something. They then e-mail you once a month to let you know what stage everything should be at and what you should be doing - sounds great for getting a beginner started. I don't know why, whether it's to do with more trace elements perhaps, but veggies always seen to do best in teh open soil rather than containers of compost. Remember that the containers will need a lot of watering in the summer, esp if you grow potatoes.

Thanks for all the answers - lots to think about and the "dig in" campaign suggestion is brilliant, as he has to watch GW by default when I am! I'm not restricting him to 3 pots by the way - I just know that he needs to start small and succeed otherwise he will just give up!

Good luck with him! lol There was an article about growing veg in containers by Monty Don in the Daily Mail on Saturday in the Weekend supplement.

I still haven't received my Dig In seeds yet.......