North West and Penelope Disick recently donated a number of toys to the Los Angeles Children's Hospital.
North, who turned three on June 15, and her cousin Penelope, who will be four on July 8, celebrated their birthdays with a joint mermaid-themed bash over the weekend before making their generous donation of My Little Pony toys.
A source told PEOPLE: "North and Penelope donated a truck load of My Little Pony's to the Los Angeles Children's Hospital. North and Penelope celebrated their birthdays at a joint mermaid-themed party this past weekend where all of the party goers had gift bags filled with Nori and Penelope's favourite toy, My Little Pony."
The youngsters' parents, Kanye West, Kim Kardashian West, Kourtney Kardashian and Scott Disick joined forces to throw a bash over the weekend where the two birthday girls donned similar mermaid costumes, complete with fishtails.
Though they had a joint party, North and Penelope each had their own birthday cake, with Kim leading the singing for her daughter, before Kourtney - who also has sons Mason, six, and Reign, 18 months, with former partner Scott - kicked it off for Penelope.
Festivities then moved outside, where the pool and gardens had been given an under the sea-themed makeover, and a number of Disney princesses joined the young guests for fun and games.
The girls' aunt, Kylie Jenner, shared a picture of herself with North and Penelope, as well as two of the special guests.
She captioned the image: "birthday girls (sic)"
The family documented the celebrations on their social media pages, and at the end of the day, 35-year-old Kim - who also has six-month-old son Saint with Kanye - plugged her 'Kim Kardashian Hollywood' mobile game with an animated image of herself and Kourtney, 37, in their mermaid outfits.
She wrote: "We're having a mermaid party today and you can join us too."
Update your news preferences and get the latest news delivered to your inbox.