It is kinda common for your lil siblings to delete something accidentally. This has happened to my Roblox account twice that I have lost forever but still I forgive my sibling. Best advice is to tell them not to touch the app and never delete it because it is helpful for you.
This is why if you make a account, get a secret notebook only you can access and write the passwords. If the account got vaporized and terminated then the pass thing ain't gonna work. Hope you have a chance to recover your account.