The invention relates to children's construction kits for assembling building toys from connecting elements. The technical result is an increase in functional capabilities, permitting the assembly of simple and complex spatial constructions with dynamic properties. This technical result is achieved by virtue of a building toy consisting of a set of flat shape-forming and decorative modular elements made of a flexible resilient material and having fastening elements attached to the surfaces thereof, said fastening elements forming detachable joints capable of holding together connected portions of the surfaces, wherein each of the fastening elements takes the form of the centre of axial rotation of at least the held portion of the surface of a connected modular element, and each of the shape-forming modular elements has on its opposite surfaces at least one coaxial pair of fastening elements which are rigidly interconnected and have oppositely oriented mating surfaces.