Adapted from a recipe in Jane Grigson's Fish Cookery. She uses the ink, I don't, mostly because I usually freeze the squid (or buy it frozen in a five-kilo box) which makes it very hard to get the ink sacs out whole. Also, the added ickiness makes teenaged girls shriek too much for comfortable cooking.
It's best to use smallish-to-medium squid, about 4 inches long (take your ten-year-old to the market and measure by their hand). That's large enough to actually taste of something and to be easy to clean, and small enough to be tender.
This amount serves two adults and three children, so probably four adults with average appetites. Good accompaniments are ciabatta or any other firm crusty white bread, and a substantial green salad made with red wine vinegar.
Fry the onions in oil until they start to brown a little. Put the squid in (beware of spitting, even if you dry it very well there's a lot of water in it) and fry until it's evenly white and curls up.
Add the tomatoes, about a teaspoonful of tomato concentrate and a glass of red wine, preferably something strong and Mediterranean.
Stew this, uncovered, for about 25 minutes (longer if you had large squid), then taste and season with salt, pepper, paprika and a pinch of sugar to bring out the tomato flavour.
If the sauce is too thin for your taste, fish out as much of the squid and onions (the tomatoes will have disintegrated for the most part) as you can and boil it down, then add the solids again. If it seems bland, a drop of wine vinegar (not too much!) will perk it up.