I'd suggest looking into the blind-box vinyl toys section of your local internets for zipper pulls. They're more expensive, but I'm afraid the beaded sort might be more likely to be eaten alive. The vinyl ones are also (usually) surprisingly oversized, which might be just the ticket for actually helping the child-zippy part. There's lots of cute ones around...check out these, or try searching for MUNNYs or just vinyl zipper pull.

http://www.doe-sf.com/index.php?act=viewProd&productId=1897&catId=224

http://www.3dretro.com/shop/index.php?main_page=product_info&products_id=1223

If the clasp breaks, use a zip-tie to reattach. The plastic/vinyl bit would break before the zip tie will.

You might also consider using a small luggage tag + zip tie...you could write your phone number and other important "If I run away" info on it.