The Relax Tritan Kids Straw Cup 350ml (Cyan) would likely fall under one or more of the following categories:

1. Kids' Drinkware: This is the most direct category, as the product is specifically designed for children. It would be included with other children's cups, bottles, and sippy cups.

2. Baby & Toddler Products: If the product is marketed for younger children or toddlers, it may also fit within this category.

3. Eco-Friendly Products: Since it’s made of Tritan, which is a BPA-free, durable, and reusable material, the cup might be marketed as an environmentally friendly alternative to single-use plastic bottles.

4. Health & Wellness: Since it promotes hydration and is designed for a child’s health, it could fall under wellness products for kids.

5. Lifestyle Accessories: If the cup is marketed with a fun design or trendy look, it could also be grouped under lifestyle or children's accessories.

6. Sustainable Living: Similar to the eco-friendly category, if the cup is positioned as an alternative to disposable plastic drinkware, it might be placed under sustainable living or zero-waste products for kids.