If your tama is adult, the tamagotchi wearing a backpack when school is about to restart after the mid-year break. You can see it at August 15th -> September 8th.
Yes, Mametchi&Memetchi is right, this is just an animation, and nothing to worry about! The new tamagotchi have some amazing holiday animation, but I'm not gonna give it away! Just check on it frequently, and you never know what you'll see!