I recently subbed when 4th graders were going to Ag Day at our fairgrounds. Three or four other teachers went too so I wasn't alone. The main thing was to keep the kids from my classroom all together and not let anyone wonder off. Don't be nervous about elementary subbing. Even tho' middle school is my favorite, elementary is easier.
You get more freedom in the schedule with elementary school if they don't switch classes. If something goes over you can let it go over and adjust other things as needed. You also get a chance to really get to know the kids since they're with you all day.
I'm in the system as a high school sub, but, sometimes, when there are no more HS positions available, they will ask me to go to an elementary school. It's nice because you don't get bored administering the same lesson over and over again and you typically get more opportunities to actually teach and interact with the students. I've never found the schedule to be difficult to follow, as most teachers are well-prepared and have a good idea of how long each lesson will take. However, you don't get as much free time (students here only get 20mn for lunch - more like 10 when you factor in getting them to the lunch room and picking them up - and that's sometimes the teacher's only break) and you have to deal with students who are on a very different emotional level than high school students. They will try to tattle on other kids frequently and some of the younger ones will even begin to cry sometimes. Personally, I prefer working with the older kids, but elementary is a fun change of pace every now and then.
I've subbed for elementary kids twice. They were little darlings, but I definitely prefer middle and high school kids so that I get different groups throughout the day. Plus, I think my personality works better at the middle and HS level. There IS the added flexibility with a self-contained class, but like you, I couldn't help wondering "When do I get a break from the kids?" I was MUCH more tired after those two assignments than any assignment I had at the higher levels. I love the kids, but elementary just isn't the best fit for me. I have acted as chaperone on several field trips with my boys. That meant I was in charge of at least 2-3 other kids, in addition to my own. Keeping them together and in sight is the biggest challenge, but normally isn't that difficult.
