Personalized 4th Birthday Monster Truck T-Shirt. I'm Four! A red monster truck drives over the words. Great fourth birthday gift for your favorite 4 year old. Everyone loves our Custom T-Shirts! Wardrobe essential for looking good, 24/7. 5.0 oz., pre-shrunk 100% cotton. Seamless 1x1 rib collar. Shoulder-to-shoulder taping. Double-needle stitched sleeves, bottom hem and front neck. Note: greys are a cotton/polyester blend.