- Extensions can be combined with all Junior Starter Sets - Ideal extensions for children aged 3 and up, with many parts GraviTrax Junior is suitable for children aged 3 and up. Boys and girls build their own marble run worlds, which can be freely supplemented with decorations to build their own themed worlds. With the Extension My Trax, all Junior Starter Sets can be expanded. A large number of wood-bioplastic parts provide even more dynamics and action on the track - for endless building fun. GraviTrax Junior is an interactive marble run system for children aged 3 and up. Children build their own marble run world to their heart's content and can decorate it with all sorts of different themed sets. Creative building and playing fun are combined. - Extensions can be combined with all Junior Starter Sets - Ideal extensions for children aged 3 and up, with many parts GraviTrax Junior is suitable for children aged 3 and up. Boys and girls build their own marble run worlds, which can be freely supplemented with decorations to build their own themed worlds. With the Extension My Trax, all Junior Starter Sets can be expanded. A large number of wood-bioplastic parts provide even more dynamics and action on the track - for endless building fun. GraviTrax Junior is an interactive marble run system for children aged 3 and up. Children build their own marble run world to their heart's content and can decorate it with all sorts of different themed sets. Creative building and playing fun are combined. 30 parts: 2 base plates, 18 height blocks, 2 bridges, 2 straight blocks, 2 slopes, 2 large curves, 2 small curves age 3-7 years packaging dimensions 22x22x5cm not suitable for children under 36 months