The london transport website is confusing. We are going for 4 days, it gives a price for kids travelcards and yet on another part of the website it says they travel free with an accompanying adult with a travel card. Can anyone make this clearer?
Children under 11 are free on the tube and children under 16 are free on buses.
Depending on how old your DCs are, however, they may need to get a photo ID Oyster Card that shows that they're young enough to travel free (i.e. if you have teenagers). DD is 8 and doesn't need any such card yet, but I think once they get to around 11 it's wise to get one.
But if you're only around for four days and your children are teenagers, then it'll probably be less hassle simply to pay child fares on the tube than trying to get an Oyster card for them.
Also, when on the tube, it's easier to go through the wide gate bit that the staff will open for you, or you can swipe through...gives you more time to get through the gates and more room if you have a buggy etc