The nearest tube stations are Wood Lane (a 3 minute walk) and White City (an 8 minute walk). If you're coming from Shepherd's Bush station, walk through Westfield Shopping Centre and follow signs for John Lewis and The Square (a 12 minute walk).
By train. The nearest Overground train station is Shepherd's Bush station on Uxbridge Road (adjacent to Westfield Shopping Centre). It has direct services to Clapham Junction and Stratford rail station and Willesden Junction.
Westfield Stratford City Shopping CentreWestfield Stratford City is Europe's largest shopping centre. It compliments its sister shopping centre, Westfield at the other end of the Central Line in Shepherd's Bush.
Shepher'd Bush is a bit more upmarket with a bit called the Village; Stratford (which might be a bit bigger now) has more High St chains and shops. Other than that not a lot in it esp now Stratford is zone 2. If they're really keen they can go to both.
Oyster cardsYou can pay as you go to travel on bus, Tube, tram, DLR, London Overground, most Elizabeth line, IFS Cloud Cable Car and Thames Clippers River Bus services. You can also travel on most National Rail services in London and some outside London. You can also add: Travelcard.