One thing you could do is look on www.localsecrets.com/cambridge website. On there are several different categories of things like places to eat and activities. You can enter the relevant dates you are to be here and see what is going to happen. Also, the tourist office may be helpful, or the city library may have information on what is going on. Pizza Express in Jesus Lane or Regent Street are welcoming to children and offer good food at a reasonable price. See any vouchers which may be available online! I hope the weather is kind to you. If it is, you could try going on the open topped bus as it's a hop on hop off service. The riverboat Georgina is fun and you can book places online in advance should you wish. You could if you wish, go on the train to Ely and visit that city too if you like. The possibilities are endless. I hope you have a wonderful time.