An attachment assembly for securing a child safety seat to a mounting portion of a vehicle is provided. The attachment assembly may include a guide having a channel, and a metal strap positioned in the channel of the guide in a retracted configuration such that a free end of the metal strap is adjacent to a front face of the guide, a fixed end of the metal strap is secured to a side of the channel, and a body of the strap is bent along a radius so as to double back between the free end and the fixed end. When pulled in tension, the metal strap is configured to transition from the retracted configuration to an extended configuration, and the guide is configured to constrain the strap during this transition so that the strap rolls along the radius within the guide, thereby absorbing energy.