Personalized Funny Mountain Biking Gravity Joke Toddler Long Sleeve T-Shirt. This cycling design for someone who enjoys mountain biking has bike and mountains silhouette and gravity joke. A classic for Fall, Winter and Spring, these long sleeve toddler t-shirts are sure to be a staple in your child's wardrobe. Whether layered or alone, this t-shirt is soft yet durable enough to stand up to your toddler's playtime demands.