My son got out of gates at school-need advice

My son is in K, mainstreamed with an aide. In his IEP for accomodations done a year ago it stated 1:1 asst (assistant will shadow the student at a distance when leaving the classroom environment). This mostly was for times if he ran an errand with a friend but still states for her to be at a distance. Well, we were seeing increasing behaviors and other things so we had an IEP meeting 2/2. The behavior part and a couple accomodations weren't done at that time but they were going to add them, they did so by Friday and sent it home and was probably waiting to "lock" it in today when I told them it looked good. On this "new" IEP the accomodation reads "close 1:1 asst proximity when outside of classroom (recess, traveling around campus etc) within 5 feet. This is great because a lot of his behaviors were at recess when either his aide wasn't there or when she was on duty for the whole class (he gets the aide 5 out of 7 hours).

So that brings us to today (which is the day I would be telling them the IEP was good and ready to be "locked" in). My son had a field trip and I was with him. His aide happened to be sick. It was an awful day for my son, just a bad day with lots of meltdowns. I had to leave after lunch and they knew it would be a touch and go day with him. When I go to pick him up I was told that while he was at recess, he crawled through the gates and was found by the custodian standing in front of the office which is right by the parking lot in an ungated area. During recess they rotate which teachers will be outside, his teacher was not outside but 3 others were. He told me he asked where his teacher was and they said at the office so he went to get her (I think he was getting afraid of the wind...a whole other issue!). I can't guarantee this is the complete story but probably is.

So, my question, what exactly do I need to do? The new IEP is dated 2/2 but I know all of them may not have seen the new accomodation of the close 1:1 at recess. But my son's issues have been at recess for the past month and everyone knows that. Who do I need to speak to ASAP? And do I need to just have them put a protocol in place for what to do when his aide isn't there? The teacher has been pretty good but I don't think she is grasping the need to follow everything on the IEP to a T!

I understand they have to give him consequences. They sent him to the principal's office for her to tell him not to do that but at the same time it bothers me that it was their mistake.

Sorry so long and thanks for any help!
Karen