The three-minute animated short, titled The Gift, was released on TV, Disney Plus and YouTube on Wednesday 2 November.
Disney’s “From Our Family to Yours” series of Christmas adverts began in 2020 with the story of Lola, who was gifted a Mickey Mouse toy from her father in 1940.
A Mickey Mouse toy also features in the new advert, which focuses on Ella, the youngest child in the family who feels anxious about becoming a big sister.
Ella, her older brother Max and their mother Nicole appeared in the second part of the trilogy, The Stepdad, to welcome her new stepfather Mike.
In The Gift, Ella is excited for Christmas but is disappointed as her heavily pregnant mother is unable to go ice skating with her – even though Mike offers to go with her.
In another scene, Ella and Nicole are preparing to put up Christmas decorations, but Nicole breaks one of the decorations due to labour pains.
But once her new sibling arrives, Ella is seen coming to accept her new role and gives the baby her glow-in-the-dark Mickey Mouse soft toy that was gifted to her by Max at the start of the advert.
The short features the song “A Little More” performed by Jessica Darrow, who voiced Luisa Madrigal in the Oscar-winning 2021 film Encanto.
It was composed by Los Angeles-based Parkwild’s songwriters Sofia Quinn and Rose Tan.
Darrow said: “The holidays hold such a special place in my heart and what better way to come together with family and loved ones than through the joy of music?
“It was such a wonderful song to perform, and I can’t wait for everyone to see the heart-warming story which concludes this inspiring trilogy.”
Disney released the new advert in partnership with children’s charity Make-A-Wish. It is encouraging fans to donate to the charity by matching all donations received up to US$100,000 (£86,657).
Sarah Fox, vice president of marketing and communications, Disney consumer products, EMEA, said: “For the last three years, millions have watched our characters in our ‘From Our Family To Yours’ animated series, as they spend time together building connections and making memories.
“We set out to create a family unit that would resonate with audiences worldwide.
“We are truly grateful for the support we have received for this festive campaign and hope that families and fans enjoy this fitting, heart-warming final instalment of the trilogy.”
Additional reporting by PA