Restraining was just an example of the kind of force that may be considered. In this case it may be that you wouldn't have to use much force, perhaps just initiating care and ignoring the parent's protests, or removing the child to the ambulance. But if it gets physical I'm not adverse to protecting myself and the patient. This is a more drastic scenario, but letting a potentially dying child just lay there isn't an option.
1. Call for code 3 law enforcement (and possibly an extra ambulance and a fire crew if there isn't one present)
2. Quickly try to reason with the parents (probably less than a minute)
3. Get access to the patient - if that means getting them out of there, great, and if the parents try to block you, then get them out of the way. Stop only if there's a serious risk to yourself.
Have fun in prison. My livelihood is not worth it.
Edit: And what charges?
Assault & Battery, kidnapping, kidnapping with force, false imprisonment. I'm sure the DA can find more. It's not YOUR child. It's their child. They have the right to choose what treatment the child gets.