Children In Need presenters Tess Daly and Greg James kicked off the live Appeal Show with promise that they would "give everything" to return the favour to long-running host Sir Terry Wogan.
Sir Terry hosted the annual BBC charity event for 35 years until 2015 when poor health forced him to pull out.
This is the first live telethon show for the charity since his death in January this year. He passed away after a battle with cancer.
Tess said: "This is our first year without our dear friend and charismatic leader, Sir Terry.
"Sir Terry was everything that embodied Children In Need and someone we will all miss very much."
Greg, who is co-hosting the show for the first time this year, said: "It is up to us to continue his legacy."
He referred to Sir Terry's famous radio sign-off quote "thank you for being my friend".
Greg said: "That sums up the man perfectly. To return the favour, the best way to do that is to give everything tonight."
Graham Norton, Ade Adepitan, Rochelle and Marvin Humes are taking up the presenting role in Sir Terry's place along with Tess and Greg.
Eddie Redmayne, who will appear in a sketch recorded on the set of his new film Fantastic Beasts And Where To Find Them, described Sir Terry's presenting as "inimitable".
The Oscar-winning actor said: "I have such fond memories of Children in Need - growing up, I loved watching all the special sketches and performances, and, of course, Sir Terry Wogan's inimitable presenting.
"It is a charity very close to my heart so you can only imagine how chuffed I was to be asked to do a special sketch for this year. I can't wait for you all to see what we have in store."
Clare Pizey and Paul Wright, the show's executive producers, said the long-running host's presence will be missed. In a statement, they said: "This year will feel very different as the great Sir Terry Wogan is no longer with us but we will do our best to honour his memory."
BBC Western House in central London, home to Radio 2, was renamed BBC Wogan House this week in honour of Sir Terry, who first hosted the station's breakfast show in 1972.
The annual charity telethon event, broadcast live, will include pre-recorded sketches and clips along with live music performances and other entertaining segments in order to encourage viewers to part with their cash for a good cause.
The night kicked off with a live performance from the West End cast of the Disney Aladdin musical.
Performances and sketches including the cast of EastEnders, Ricky Gervais as David Brent and the stars from The Great British Bake Off are expected.
Children In Need aims to protect every child in the UK and currently supports 2,400 projects across the nation. Since its creation in 1980, the charity has raised over £600 million.
This year's live telethon effort will attempt to raise enough money to beat last year's record-breaking total of just over £37 million donated during the broadcast.