Our estate is fairly simple, with 99% of assets in a few brokerage accounts. All of the accounts are set up to Transfer On Death (TOD), thus bypassing probate entirely. My wife and I have each named each other as primary beneficiary and our minor daughter as secondary beneficiary on all of our accounts.
In the extremely unlikely event that both my wife and I were to die at the same time, sometime during the next 8 years before our daughter becomes an adult, the state would name somebody, probably a relative or family friend who would come forward to take guardianship of our daughter. You can name anybody you like as guardian of your children, but it still has to be approved by the state. If your named guardian doesn't meet the requirements of your state's equivalent of Child Protective Services, the State will find somebody else. It doesn't matter what's written in your will. The few thousand dollars in our savings account would have to go through probate, but so what? Our daughter could just choose to abandon it and give the money to the state, as she'd already have 99% of our assets.
OP, try googling, "intestate succession (your state's name)." Here's a summary of the
rules for HI.