Water-reveal/color-changing pen sets typically include interchangeable tips such as calligraphy, standard (round), and a wide brush tip so you can create different stroke styles and effects.
Water-reveal activity pens for toddlers and preschoolers are typically chunky and easy to hold, refillable with water (no ink), and designed with safety and simplicity in mind. Sets often include interchangeable tips (calligraphy, standard, wide brush), a pump-style sprayer, and a tethered cap; they’re commonly marketed for ages around 3–7.