Hi, I believe that even if you have your children listed as beneficiaries on your life insurance, retirement accounts, etc that they won't gain access to it until they are adults...meaning your chosen guardians won't get access either unless you set up a will with a trust. I also believe that even if only one of you dies intestate, that the children will automatically have rights to a 1/4 of the assets each.
My aunt died intestate a few years back and my two adult nephews sued my uncle for "their" portion of the estate. He ended up settling with them.
Also, be careful when doing your will that you don't unintentionally disinherit your kids. This happens all the time. i.e. one parent dies-gets all the assets-she re-marries-then dies and then her new spouse gets all her assets, etc