Notorized Paper giving parents custody

What is the name of your state? az

My husband is 31, I am 25 we have 3 small children 5,3, 15 months-
In June of this year I had typed up a paper giving my parents 48-and 49 yrs old, and both my sisters 27 and 21 custody and medical rights of our children if anything was to ever happen to my husband and I.
This is a notorized letter.
For our saftey and protection if anything was to happen to us will the courts allow this letter or should we do a will- ?

We own nothing except a car.

My husband has no family. his mom died at 54 Heart Attack, His dad is outa his life since he was 11.
My family all lives down the street from me this is no joke ( I live on one corner , my older sister lives on the other, and my little sister lives around the block. parents live 10 miles away ! )

My husband works at a Insulation Manufacturing plant- Can Cause health problems-
(He's not here right now so I can type this- He complained to me the other day first time EVER that he was having chest pains REFUSED to go to the hospital)
I know that if he was to ever die on me I would have to go back to work ....
Now if he was to get killed at work I would be set, he has a life insurance policy at work that pays pretty well-

Even though we are very young still should we go ahead and do a will for our family and our children - So that "everyone" is happy ?

Everyone needs to execute a will. Many people think that just because they have few assets it is not necessary. What they do not consider is the problems they are leaving behind for the ones who have to sort everything out. Probate is much quicker and easier if there is a will.