"It sounds like you are trying to put the HSA info on the dependent's return. It would go on the mother's return since it's her employer and W2."

Oh, that might be a good mind-read. I thought an Adult child's employer contributed to an HSA in the name of the child, but the policy is the Mother's. Since HSA accounts are owned by the policy holder, you can't open an account for the child just because the employer offers this benefit. And as Bill pointed out, a dependent also doesn't qualify.