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You would not be under any legal action according to the IRS or the state.
However, you may be in partnership with the other persons also named on the account and the custodian of the child.
They may not agree with your actions, and might bring law suit based on theft of funds.
Since this is not set up as a trust or other legal entity, it becomes a matter of what the other persons on interest on the account treat your partnership and what agreements you might have.
Under the best circumstances, this should have been set up as a special needs trust. Then the trustee and the beneficiary would have a say in how the money was spent.
In this case you have to deal with it on the basis of partnership and agreements, oral or written.
The risk is that of a civil lawsuit by the others.