GraviTrax Junior - Extension TraxGraviTrax Junior Extension Trax gives children from the age of 3 a child friendly introduction to themed marble track worlds. The GraviTrax Junior Extension Trax set is perfect for taking those first builds even further. With 35 extra track elements, columns and platforms, this expansion gives young engineers more ways to twist, turn, climb and race their marbles across the landscape. The chunky, easy grip pieces are designed with younger learners in