Typically, you want a big, bang, boom for both your openers and closers.
This is not necessarily true, particularly for openers for kids shows. What's far more important in kids shows that opening with a "big, bang, boom" is connecting with the kids, creating a relationship, establishing that you are all there to have fun, and getting them laughing. Of course, there's also the importance of warm-ups...ways to accomplish those objectives before any magic actually happens. The sudden surprise of a Disappearing Cane might initially grab their attention, but it doesn't establish an enduring connection.
I've used a variety of things for "openers," including the Flower Wallet, the Crystal Tube (aka Blow Tie), Acrobatic Silks, a Blendo, or the Dream Bag (part of a silent routine done to music). No "big,bang, boom" in any of those pieces, really...but lots of fun, interaction, humor, and opportunity to connect with the audience and let them know what they are in for. Of course, the presentations I use have a lot to do with that, as well.