Medical expenses for dependents are an itemized deduction. You can only deduct the total amount of medical expenses in excess of 7.5% of your adjusted gross income. You can get a tax benefit if the total of all your itemized deductions is greater than your standard deduction.
Here is an explanation of standard vs itemized deductions: https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-credits-deductions/standard-deduction-differ-itemizing-deductions/L4CTwCJ3L_US_en_US