With orders of $25 or more, Amazon offers its Prime members the Bell Toddlers' Frozen 3D Olaf Multi-Sport Helmet, model no. 7067910, for $6.06$5.82 with free shipping. (Non-members can spend $49 to bag free shipping.) That's $11 below our December mention and the lowest total price we've seen. (It's a current best by $11.) It fits head sizes 48cm to 52cm and is designed for bicycling and skating.
Also available with orders of $25 or more is the Bell Toddlers' Frozen Olaf Sunshine & Happiness Helmet for $6.41$6 with free shipping for Prime members. That's $14 off list and the lowest total price we could find. It features high-impact reflectors for visibility and extended rear coverage for added protection.
Note: These items are part of Amazon's "Add-on program" and can only be purchased with an order of $25 or more.