Which Culture celebarates 7th Birthdays with something special

[Eve]

A mum at school this morning asked me if my son could participate in her daughters 7th birthday celebrations as they are significant for her.

He will need to have dance lessons and wear a special suit, which she will organise and teach him. The girls will all be in ballgowns

It sounds wonderful for him but I would like to know more about it so I can talk to him about it and discuss what to expect.

don't they have big 7th birthday celebrations in japan?

..not sure it is Japan, their teacher couldn't recall which nationality but said not Japanese

I found this:- but it is Japanese.

The Shichi Go San or 7-5-3 Festival is one of the uniquely Japanese festivals. Boys who are 3 and 5 years old, and girls who are 3 and 7 are taken to a shinto shrine, often in their first kimono, and the parents pray for their continuing good health and prosperity. The numbers, especially 3 and 7, are lucky numbers in Japan, and until the 20th century Japan was a thoroughly feudal nation with a higher childhood mortality rate. Since bacterial pathology was then unknown to them they often blamed death on evil spirits, and when the kids became 3, 5, and 7 years old they thanked the gods for their children's good health. A sweet candy called chitose-ame is also often bought for them, in a bag with cranes and turtles, 2 more symbols of long life.