How disappointing for you all. Did you over-water perhaps? Try again next year as sometimes weather conditions cause all kinds of unexpected problems which make gardening a challenge. Tomatoes are normally quite reliable. A few runner beans up sticks might be worth trying as you can buy different varieties which have pink, white or red flowers which the children might enjoy. I'd give carrots a miss as carrot fly can be a real problem. How about courgettes, picking them when they're no longer than 4" long, when they make healthy crudities when raw, to dunk in dips. Lettuces are easy to grow too and there are lots of red leaved varieties now to add colour and interest.Radishes grow quickly but usually attrack slugs unless you grow them in grow bags. Good luck!