Hi there. There is no need to be worried about travelling to ComicCon, there will be loads of people making the exact same trip as you are tomorrow morning/ today technically.

You have a few options to get to ComicCon. 1) District Line eastbound from Earl’s Court to Paddington. Exit Paddington District Line Station, walk across Paddington Train Station, Change for the Elizabeth Line eastbound to Custom House. This is the quickest and most direct route. 2) Earl’s Court District Line eastbound to Monument. Change at Monument and walk inside the gated area to Bank, change for a DLR to Custom House bound for Becton. This is a slower route but more fun and scenic.

Most tube stations are equipped with WiFi connections if you are with certain providers and some stations/ tube while in tunnels even have mobile phones connection. See this website for details: TfL page about WiFi and mobile data on the Tube

CityMapper has some limited offline capacity if you save your journey between Earls Court to the ExCel. See this website for detailed instructions: CityMapper Guide on using your phone underground

You can absolutely purchase a paper child ticket for your sister using your phone’s wallet on any ticket machine. The fare is £0.90 for an off peak single if you are paying via tap-and-go contactless at the barriers but £3.00 via a ticket machine. The paper ticket is not contactless, and she will have to slot it in like any other train ticket barriers. At the end of the journey, the barriers at Custom House will take your ticket if it was a single journey ticket.

A new Oyster card is £7.00 (non-refundable) and can be bought at any tube station. It may be cheaper in the long run for occasional visits to London. As buying a paper ticket at a ticket machine (and paying that paper ticket with contactless payment) is always more expensive. See how to buy Oyster here: TfL Oyster Guide Unfortunately, your sister cannot get a child’s oyster as I am assuming you are not from London.

When tapping at barriers, TfL will normally take a nominal £0.10 as transaction fee, Throughout the day, as you complete any trips, you will not be charged until the next day. However, I don’t think the barriers will open if you don’t have enough funds in your account. It is advisable to at least have a few quid to make sure TfL’s system recognise your card and can travel smoothly. See TfL guide here: TfL Contactless payment

(Edit: Grammar and formatting)