If you accept the offer, you'll receive 1,000,000 dollars every January 1st for the remainder of your life. This money will appear in a magical bank account that no one else can tamper with. You can access this money with any credit card you aquire (regardless of who it belongs to), or by withdrawing cash from any ATM (no matter if it's broken, a specialized bank, etc.)
However, upon accepting, you're immedietely physically turned into the a child. The magic randomly chooses an age between 5 and 13 years old, and reverts you to what you looked like at that age. You retain all of your memories, knowledge, and intellectual capacity, but you will look this age forever.
You will be seen as a child in the eyes of the law, and your birth certificate (+any other documentation) will magically update every year to keep you at the specified age. For example, if you were reverted to 6 years old, your birth date now would say 2020, but next year, your birth date would be listed as 2021, so that you would still be 6 years old in 2027. Everyone who knows you now will remember that you existed, but they won't believe that you've been transformed into a child, and won't recognize you.
You never physically age, but your lifespan remains the same. You can still get sick, and experience typically elderly conditions like arthritis or dementia. You'll still die whenever your natural life would have ended. However, when you initially transform, any disease/condition you didn't have at that child age disappears. For example, damage from smoking (assuming you werent as a kid) disappears. You could still re-damage your lungs later, but it's one fresh start.
If you decline, life goes back to normal, but your current phone never charges more than 97% :)