Family coming to stay in London

[Sassybynature]

Help...I live on the outskirts of London. Family from Italy will be coming to stay with me for just two nights in London during half term and I am wondering how best to make use of just two nights in London.
It will be two adults and a nine year old boy, i want them to see as much as possible in just two days. So what would be the best itinerary, where should we start. The obvious places Buckingham Palace, Tower of London, Big Ben. Anything I should include for the nine year old boy that would make the trip memorable for him. Any great tips for eating? I was thinking Byron Burger or Five guys.
I am stressing, I have been asking them to come for years, now they have finally decided to make the trip I am worried of getting it wrong.

I'd recommend getting Big Bus Tour classic ticket. On the bus, do a complete lap of the Red Route without getting off. It takes just over 2 hours and includes Westminster Abbey, Trafalgar Square, Covent Garden, Big Ben, Mayfair, London Bridge, Hyde Park, Tower Bridge and Buckingham Palace. There's live commentary in English but Italian is an option for the pre-recorded headsets.
The ticket also includes a one-way river cruise along the Thames from Westminster Pier to the Tower of London, or vice versa. I'd start and finish the bus tour at Westminster Pier so afterwards you can catch the boat straight up to the Tower of London. If you're up early, you could be done with the bus tour by mid morning and be at the Tower for lunch. The are about 3 different cafes and a kiosk where you can buy food. Then allow 3-4 hours for the Tower. After you're done, head over Tower Bridge and walk along the river to Southbank in time for dinner. You could then go on the London Eye in the evening if you have time . At weekends it's open until 8:30.

If the 9yo is a Harry Potter fan, he might appreciate going to Kings Cross to see the trolley in the wall and visit the shop at Platform 9 3/4. It's open from 8am so could be done early the second day. Afterwards I'd head to Leicester Square for the Lego store and then walk through China Town before going to Covent Garden. Try and include some time to browse around Covent Garden and for an afternoon tea. If there's time in the afternoon or evening, you could see a show.

RiceKrispie, thank you so much.
That is exactly the type of itinerary I was thinking of but couldn't work out the timings or placing of the main sights. I will check if he is a Harry's Potter fan, another great idea. The shows will all be in english, so unfortunately he or my cousins wouldn't understand them. Unless there is a cirque de solely type show on..mmm wil take a look.
Thanks again!