Helmets should not have animals on the outside
Summary: Some helmets for kids have cute little animal parts on the outside--noses, tails and more--but in some cases those detract from the helmet's ability to slide well on pavement. We are all in favor of kids having fun, but if they must have an animal helmet pick one whose animal parts come off readily.
In recent years child and toddler helmets have appeared with rubber animal ears and noses mounted on them. Some go well beyond that, with high ridges, mohawks, horns and other projections. The decorations are cute, but they must detach readily to avoid being a hazard in a fall.
The CPSC child bicycle helmet standard outlaws projections of more than 1/4 inch (7mm) that do not collapse or break away readily when tested. CPSC wrote that into their standard because lab studes have shown that projections can cause a helmet to snag in a fall and increase both the strain on the rider's neck and the g's to the rider's brain.
The animal decorations usually collapse partly, but the remaining lump for many is higher than 7mm. Most of the animal projections are soft rubber, but some have a harder core, and many do not readily detach. We have a page up on sliding resistance to explain in detail why we think helmets that would not slide easily on pavement present a hazard, and do not recommend them.
We have put up the lab study that established the value of a round, smooth, slick outer surface if you want to see the scientific data. And we have study on Chin Strap Forces in Bicycle Helmets confirming that a shell that does not slide well increases the jerk on the chin strap.
Disclaimer: nobody has gathered statistics on whether injury rates are higher in animal helmets. Our comments above are based on science and the knowledge that sliding on impact lessens injurious forces to the head and neck. A helmet with animals on the exterior is always better than no helmet at all.