We just finished our annual play. I was pretty satisfied with everything, except the scene changes. We are very slow. There is not fly, and the wings are pretty narrow, so we spend a lot of time trying to shuffle things around. Any suggestions on ways to speed up, besides just not having anything on stage.

Think choreography. Make sure each item has one or two kids (if needed) assigned to it. Before each scene change, have the kids stand in a position that is as close as they can to where the item will be placed or removed from the stage, then have them close their eyes and look away from the lights until the blackout. It helps to get the eyes adjusted to seeing in limited light. When the lights go out they will move their items in their predefined choreography so that they don't crash into each other. As soon as their item is placed, they should leave the stage quickly and quietly. 

Blackouts or curtains can be magical if the time is minimal. It is cool to see the stage go black and then come back with a completely new scene a few seconds later. I've also seen beautifully done period pieces where the light never changed. Pretty much anything can work if you design your scene changes for efficiency.

If you can't do it in less than 35 seconds, then don't do it.  Figure out an alternative set design.

Majicwrench and David McCall are both one hundred percent correct.

It really helps to have (appropriate) music playing, and a choreographed approach is the only way to go.

Recently saw a production of "The Shape Of Things" that required longer than normal set changes - not because the set was complicated, but because the lead actor had to undergo physical transformations (weight loss, hair style, clothing changes, etc.) and there was no time for it except for the scene change times.  The director worked out a whole mimed secondary story with the set change crew - working together, having a falling out, making up, and getting back together.  It worked really well, and I don't think they had any scene change longer than a minute and a half, but that was a unique situation.  Under ordinary circumstances stick to the 35 second rule.

I'm a fierce proponent of "less is more."  The audience will always be glad to meet you more than halfway.  They're not as dumb as some directors think they are.

Consider dividing your stage into upstage and downstage.  Close the mid curtain and play a scene downstage while changes are occuring upstage.  Or use a scrim to divide the stage and project backgrounds on the scrim for upstage scenes and look through the scrim (or travel it off--don't use sharkstooth, it doesn't travel well) for the upstage scenes.