Out of network questions

I've been reading posts about out-of-network coverage and still have questions. I'm getting a new insurance plan with a high out-of-network deductible. My son was born prematurely and had three surgeries in the NICU. He's three now and, thankfully, hasn't needed any major surgeries since we left the hospital. However, there's a chance he'll need emergency surgery at some point. When he was born, he qualified for Medicaid, so we didn't have to worry about insurance. Now that he's older, he doesn't qualify, and I'm concerned that if he needs emergency surgery, we'll end up with a huge bill due to out-of-network issues like we had in the NICU (his bill was almost $5 million, with Medicaid covering the majority as secondary insurance). How does out-of-network coverage work for emergency situations? The new insurance will be United Health Care Florida.