When I worked in ER it was a "joint" decision. The parents did have some say in what we would do, but we also had to discuss the possibility of "convincing" them of the way it WAS GOING to happen. :uhoh21:
As for assault, if the parents are in agreement I don't know if that's even an issue here in the states. You're doing it for the child's betterment and most times they cannot comprehend that.
As for waiting... if you're doing sutures you can't wait until the next day. For the most part 6 hours was our limit. If it had been longer than that they wouldn't do it. You wait until the next day they don't get sutures.
We did use a blanket and papoose them. Sometimes we even wrapped them and taped them. We also had a board that we could use. I certainly don't think it's "crue" or even "harsh". They need the treatment (these wren't used for "iffy" cases) and somehow it has to be done.
As for the parent holding them, most of the times that's a big no no. In nursing school we were taught that if you let a parent hold the child they can look the parent like "why would YOU do this to me". We even talked about having parents wait outside for really invasive procedures so that teh child wasn't thinking "why would YOU let them do this to me". After the procedure the parent comes in and is the hero becuase everything stops.