When a single parent passes away, leaves no will, yet has a bank account, insurance policy, are grown children responsible for her debt or how will hospital and doctor bills be satisfied?

The only persons responsbile for debt are those that sign off agreeing to pay it. So unless you and your siblings agree to pay your parent's debt then you aren't responsible for it.

However, your parent's estate IS responsible for the debt. Any outstanding debt has to be paid out of the estate before it can be distributed. So whatever was in bank accounts needs to be used to pay outstanding debt.
If the executor of the estate does not use the cash assets to pay the debt they can be sued over it.

Insurance policies are not part of the estate and their proceeds go to the beneficiary of the policy.

Even if the estate is small and no will exists. These facts hold true.