One should not rely on the advice of untrained relatives or friends who are not up to date on Montana laws regarding wills. In your will you nominate a guardian for the children and conservator of the assets. Guardianship provides for the children's care until they reach maturity. Conservatorship provides for management and distribution of the money and property left to children until they reach the age of maturity. One person can perform both functions, or you may name one individual guardian and another conservator.
Some parents choose to leave the money and property to the children in a trust.
A trust document states how you wish the money to be spent, who should be the trustee, and when the trust should terminate. One advantage of a trust is that it can terminate at any age you indicate in the trust document. That age could be well in excess of the age of majority, which is currently 18 in Montana. The trustee has the responsibility of writing out the checks for the children's living expenses, education, and other costs. You could name a trusted family friend or relative who has money management experience, a bank, or a trust company as trustee.