Brantford, Ont., teen Kaitlin Coghlin had a very happy "un-birthday" on the weekend.

Six months ago, she had no friends. But on Sunday, ahead of turning 18 this Wednesday, Coghlin couldn't stop smiling as she posed for pictures with princesses, stared down Batman and hugged police officers.

The "un-birthday party" was held as a celebration for Kaitlin and others who don't otherwise get invited to parties.

Coghlin has Williams syndrome, a rare genetic disorder that presents differently in various individuals, but generally, can affect brain development, combined with physical effects or problems, including lack of co-ordination, muscle weakness and possible heart defects, according to the Canadian Association for Williams Syndrome.

Earlier this year, Coghlin was feeling low — she had discovered she wouldn't be able to graduate from high school for a few more years, and then was expecting to have a birthday with no friends around. So her mom, Nicole Callander, put out a call on social media, including a special Facebook page, asking for birthday cards to make her daughter feel special.

Prime Minister Justin Trudeau and Hamilton rock stars the Arkells were among those sending their best.

But among the hundreds of notes, hand-drawn pictures and well wishes from around the world, Coghlin also received messages from parents who were feeling her pain, because their kids also never received invitations to parties.

Kaitlin’s mom, Nicole, said she was contacted by hundreds of parents who said their kids had also never been invited to birthdays or had no friends who would come to a party. So she created the “Unbirthday Party” where people could celebrate together and make new friends. <a href="https://t.co/B7CdUAzOGs">pic.twitter.com/B7CdUAzOGs</a> —@DanTaekema

Looking over the mountains of cards, Callander said she felt she had to share the love, and the idea of an "un-birthday party" was born.

"The theme is birthday, but at the end of the day, it's just that we want kids to have friends. We want them to belong and we want to build up their self-worth, and this was the perfect avenue to do it."

Something to celebrate

On Sunday, Mohawk Park was packed with jugglers, emergency personnel showing off fire trucks and police motorcycles, and hundreds of party-goers in face paint. Some 120 birthday kids were among those celebrating with Coghlin.

Yoga teacher Sasha Walsh brought two students, Nila and Vivi, who typically celebrate their birthdays with family or class members to avoid the letdown of hosting a party where nobody shows up.

"It's hard when you're that age and a young lady, and not like everyone else."

Sasha Walsh, centre, poses with Nila and Vivi, two of her yoga students, who spent all week looking forward to the celebration. (Dan Taekema/CBC)

Nila has autism and attention deficit hyperactivity disorder (ADHD); Vivi has anxiety issues, said Walsh. But the un-birthday gave them both something to look forward to all week.

"To bring them somewhere where, not only was it people like them who have been through the same experience, but to just come and have a day to hang out and party, was great," said Walsh.

The start of a movement

Mayor Chris Friel described the party as "Brantford at its best." He hopes the idea catches on in communities across Ontario and starts an inclusion movement.

"It's not that people intentionally exclude; they just don't always know how to include," he said. "The opportunity to offer this, to show people how to do it … this kind of event is something that will spread."

Brantford Mayor Chris Friel presents Kaitlin with a certificate and a special birthday card signed by everyone at City Hall. (Dan Taekema/CBC)

Organizers aim to make next year's celebration a citywide festival, said Callander, who admitted planning a party that was bigger than her wedding was a bit intimidating at first.

But seeing the change in her daughter after just one day of being surrounded by love and happiness showed her the power of a little kindness.

"At the end of the day, nobody should be excluded because of a disability. In fact, my goal is to make sure that for everybody with a disability, everyone can see that they have amazing abilities instead.

"Six months ago, Kaitlin was crying because she had no friends, and she wasn't included and she was so lonely … today she feels like the biggest superstar in southern Ontario."

Cinderella (Jodi Nagy) and Moana (Sabrina Reid-Smith) from Princess Parties and Appearances were on hand to take photos with party guests. (Dan Taekema/CBC)

Kaitlin, who said her favourite part of the day was seeing the fire trucks and police cars close up, is already looking forward to next year.

"It's good. I like it!" she said with a wide smile. "Thank you for everyone who came."