After having asked for additional material me my three year old daughter, I came across the official kits of Theo Klein. For example, this one: MultiTech 8498 vehicle design Theo Klein 8531 - Technico Basic Set II, construction kit 94 pieces Theo Klein 8585 MultiTech Construction set in Even if it is, interestingly, not all mentioned explicitly in the Amazon product description, the boxes are obviously all compatible with each other.