Here's a link to several items on the market right now:
http://earplugstore.stores.yahoo.net/chearpr.html
My husband likes to race his cars at a very loud track and really loves it when we come out to watch. We did some research and found that the earmuff style of headsets are probably the best (and only) thing out there suitable for babies and toddlers. All the smaller earplugs and other devices say 'for use by children 5 (or 7) and older.'
Drawbacks: The earmuffs look huge and clunky and you have to get your little one used to them beforehand so they won't just keep knocking them off their head.
I didn't want to bring our baby unless she had some kind of protection, so we sprung for the earmuffs. We spent some time getting her to think they were as cool as her sunglasses, and the rest is history. They really do work.
Hope this is helpful.
- E.