Mahina Mermaid Li'l MerFin Swim Mono-Fin (Aqua) The Li'l MerFin is an ultra-lightweight fin which has an adjustable foot strap, which makes it a one-size-fits-all for children between the ages of 6 and 12. Designed for those wanting to test the waters and put their little toes in the shallow end to discover what all the fuss of Mermaiding is about. A dress-up toy that can be used both in and out of the water, Li'l MerFin lets little girls imagine they are a mermaid and even swim a lap or two like a mermaid if the foot strap is pulled tight. For safety reasons, the foot strap will release quite quickly when used in the pool, which is part of the adjustable single foot strap design. The Li'l MerFin is perfect for the pool, allowing Li'l Mermaids to play their Mermaid games in safety and build water confidence, while inspiring their imaginations.