Child custody

I was working in USA on h1b visa. My wife also was in USA on dependent visa. We have 4 year USA born and USA citizen child. 1.5 year back we came visited India and wife wanted to stay 3 more months India with her parent. So I agreed and went back USA alone. My wife joined govt job and she don’t want to come back USA. She was settled in USA for 3 year. She lied in address, my income and hided the USA citizen kid in documents submitted during joining. My kid has Heath issues gone through multiple surgeries but didn’t have expected result. I am planning to take my kid USA considering his citizenship status, health and education. My wife is not ready leave job and come. Same time when kid was with her, what ever the financial support I am making was not reaching to child in my absence . But she agreed to give up child custody to me for taking my kid for treatment. Tentatively it can go up to 2 years. For minors kids both the parents approval required in many occasions. My kid needs medical attention as soon as possible. Please guide me on this.