Is my husband halachically able to bar me from using money for something I deem necessary and important, such as medical care for a child? He is convinced that this specific kind of medical care will not be effective in this instance, but I want to give it a try. Since it is halachically his money, is he allowed to refuse me the money, or is he required to trust me in my taking care of our children?
When a woman gets married, she given a kesuba by her husband. The kesuba obligates the husband to provide his wife (and children) with basically the things that they need. It includes an obligation for him to feed her, cloth her, pay for her medical bills, provide her with housing, and if need be to pay for her ransom. It even obligates him to provide her needs after she departs this world, such as paying for a burial plot etc. It also includes that after he dies, she can live off his estate, and that her children will be fed from his estate. On the other hand, chazal gave the husband four things from his wife, among them are lost items that she finds, and her wages. Therefore, in general the money in the house is under the jurisdiction of the husband.
The difference in opinion between you and your husband regarding this particular type medical care, is not a matter of trusting you, and something personal, but a difference in opinion, which is quite common in a marriage. When a child needs medical care it is very stressful for the parents, as they both want to help the child to the best if their capabilities, and each side has to trust each other. This is especially challenging when both of them are under stress.
Hashem should send your child the correct medical care that is needed and help your family out in every way.