This is my 2nd year doing carnival and last year I got some of the best advice I could get for our K-5 kids regarding inflatables. We did not do the jump house/bouncer/moon walk. As noted above, the "monitoring" was too much of a hassle ans someone was always getting whacked by someone bigger. ugh
We opted for a 3-in-1 slide/climber inflatable. It was a perfect fit for our K-5 kids. We also made it just 2 tickets, like all of our games, so it would be a repeater. It was a huge hit and more than paid for itself.
We also scored with the food by having Chik-Fil-A on site. they have a fundraiser program wherein they come to your event, set up a tent, sell & serve the food yummy!) and we get a cut of the profit. No dads grilling or mess to clean up!
This year we are fine-tuning and doing unlimited play wristbands for everything except food, photo booth, and the sponge throw (3 throws/$1 for charity). No tickets to sell, count or run out of! We also contacted the local Shriners so we'll have clowns
Another idea, we are using middle schoolers and drill team volunteers. They man the work the event and PTA makes a donation to their group. That way parents can enjoy the carnival with their kids!
Hope some of that is helpful! Good luck on your event!