I like to make an unfussy rice and tomato soup (for myself, too, sometimes, especially when I'm trying to balance out my characteristic gluttony) by diluting a good, bought tomato sauce with water, adding a handful or so of basmati rice, and cooking until the rice is tender, about 8 to 10 minutes. With children it makes more sense to leave the soup fairly solid, but you can add water from a boiled kettle toward the end of cooking time if you want a thinner soup rather than liquid tomato-rice stew. Grate Parmesan on top and eat - with bibs.