Aglians wrote:
Which is the cheapest way to get Bayswater from Luton aiport? We are
adult and two 14 years old children.

Probably Easybus www.easybus.co.uk
Runs Luton Airport - Victoria Coach Station.
You could take the Circle Line Tube from there to Bayswater.
(Bit of a walk to the Tube station)

The GreenLine bus service stops at Baker Street Tube, so would be more
convenient. Tube or short bus journey to Bayswater from there.

On arrival in London, buy some "PrePay Oyster Cards" (adult and two
child) at any Tube station. You will need to give a £3 deposit. The
Oyster Card saves a lot of money versus cash fares.