Hi - I am going to be flying with my 5yr old son from the East coast of the US over to South Africa. We have the option of either a 12hr layover in London or an overnight stay. Basically it will be a ten hour flight from here to London - then another ten hours to South Africa. My son is a good traveller but I'm not sure what would be the best way to do this. Could we stay happy at Heathrow for 12 hrs? Is there much to do? Also would there be somewhere to store luggage if we did a day trip from the airport? Any experienced travellers have advice on what would be better? I'm tempted to overnight but thinking that by the time we fly back to the US I'd just want to get on with it and get home. Any advice? Thanks.
I don't think there's enough to do to keep a 5 year old busy at Heathrow. Depending on timing of your layover (i.e. sleep time), you my want to consider an overnight stay. If this is not an issue, I suggest leaving Heathrow, take the 20 min. Heathrow Express train into Paddington station and do some exploring in London instead of staying inside the airport the whole time.
Good luck! Sounds like you have a great trip planned.

Heathrow does have a luggage storage facility, think around GBP2 per piece.
Think you're right about the return trip, just do it in one go.
Have a great trip!

Either way can be good - but you have to see the stop as a good part of the journey, rather than a delay in getting home. I recently took both my kids (6 and 3) between NZ and India. The flights weren't as long as yours but it took us 4 flights and a10 h stopover in Sydney. We spent most of the stopover in a museum and it was great (although, admittedly the Australian Museum is probably the best museum I have ever seen for kids). The kids were very happy and actually saw the whole trip as an adventure rather than the ordeal I was anticipating.
I am usually tempted to stay overnight on a long stop-over so I can get some sleep (the kids sleep just fine on the plane), but don't usually do it because of how much luggage I need to carry with me for two young kids. With one 5 year old, it should be relatively simple. On the other hand, you could just go out of the airport the whole 12 h, keep busy and sleep well on the second part of the flight. I agree that staying in the airport isn't a good idea - I've done this twice in Malaysia (for 12 h) with the kids and it is a long time if there isn't much to do (and we had a transit hotel room!).

Hi,
We did something similar when my daughter was 4 years old. SFO to LHR / LHR to Dar. We chose to have just a 12 hour layover. What saved us was using the YOTEL which is in the airport. It allows travelers to pay by the hour. It provides a bed, a bathroom (toilet/shower), a nice television and computer hook up. It was perferct for a nice rest and shower to prepare for the next flight.
It was also really convenient to get to and was in the same terminal as our departing flight was in.
Hope this helps and good luck. I think you will have a great time.
I've travelled with my son since he was a few months old, and I've always found that going straight through works best. We had a 12 hour layover for economic reasons earlier this year, and it's the absolute opposite of relaxing: you have to get out of the airport (or stay in the airport) and then get back to it. And it doesn't leave you enough time to do anything productive.
If you can't connect straight through, then I'd try and make the stopover on the way out more than an overnight, so you can see something of London.