The ISPCC's Childline listening service answered 723 contacts from children on Christmas Day and night.
Issues raised included Covid-19 restrictions, mental health difficulties, and family tension.
Domestic violence and the impact of excessive alcohol intake were also raised.
Childline said that the service answered 615 calls, texts and online contacts between midnight on Christmas Eve and midnight on Christmas night.
There were 108 contacts across all service options combined between midnight on Christmas night and 6am this morning.
35 volunteers worked on Christmas Day “to ensure the service remained active for any child or young person seeking a listening ear”.
“While many homes fill with love and warmth on Christmas Day, we know from the children who contacted Childline yesterday that the magic of the season does not reach every child,” said ISPCC Chief Executive John Church.
“For some, what ought to have been the most joyful of times can be the most frightening.
“Never before has a year presented so many challenges to so many children. They have borne the brunt of huge upheaval, with extended school closures, separation from their grandparents and other loved ones and more.
“In many cases, there has been anxiety at every turn – and they have picked up on this”.
Mr Church praised the “extraordinary” volunteers across the country “who have helped to make sure that every child and young person has somewhere they can turn 24 hours a day, every day, at this critical time”.
“It was particularly striking yesterday for our service to hear from children and young people contacting us to thank us for having been there for them this year when they may have felt as though there was nowhere else they could turn,” said Mr Church.
“They spoke about how they are now hopeful that 2021 will be a better year for us all. Contacting Childline can be life-changing for a child or young person – our volunteers make that difference”.
He added: “None of this would be possible without the sustained generosity of the general public, who have stepped in at a time when many of the vital fundraisers on which we rely each year could not take place.
"We are sincerely grateful to all of the individuals, communities, creatives, schools, corporates and everyone who supported us throughout 2020 and helped make sure Childline was always here for every child and young person”.