Tess Daly has promised an “amazing night ahead” as she opened the show for Friday’s Children in Need.
A Weakest Link celebrity special, Blue Peter presenters doing Strictly Come Dancing, a singing EastEnders cast and Doctor Who will all feature.
Graham Norton, Mel Giedroyc and Ade Adepitan are also presenting the five-hour charity show on BBC One and Two.
More than 1,500 children will also be singing together across 10 different UK locations.
A record £46.6m was raised last year.
The show, which began on BBC One at 19:30 GMT with Tess and Ade, will include some of the children and young people whose lives have been changed through support from Children in Need.
Graham and Mel will take over presenting duties later on, followed by Marvin and Rochelle Humes.
Highlights will feature the steely Anne Robinson presiding over the Weakest Link. Celebrities facing her questions and cutting remarks will include actor John Thomson, Love Island winner Kem Cetinay and actress Chizzy Akudolu.
Six current and former Blue Peter presenters will don Strictly’s sequins – Mark Curry, Diane-Louise Jordan, Anthea Turner, Tim Vincent, Konnie Huq and Radzi Chinyanganya will compete for the Pudsey glitter ball trophy.
EastEnders fans will see their favourite characters sing popular numbers from classic West End musicals, while Doctor Who fans will get their first exclusive look at the Christmas episode.
There will also be music from Rita Ora, The Vamps and Jason Derulo, while Joanna Lumley will present the Sir Terry Wogan Fundraiser of the Year award to people who “go above and beyond to raise money”.
Stage stars taking part include the cast of West End show Annie – including Strictly’s Craig Revel Horwood – as well as leading ladies Amber Riley from Dreamgirls, Beverley Knight from The Bodyguard and Cassidy Janson from Beautiful: The Carole King Musical.
Children in Need is the BBC’s UK corporate charity and raises money for disadvantaged children and young people around the country.
Children in Need will be on BBC One from 19:30 GMT until 22:00. It will switch to BBC Two from 22:00 until 22:40, before returning to BBC One from 22:40 until 00:30. There will also be a One Show special from 19:00 until 19:30.