Adaptive serious mathematical games in kindergarten were used to investigate whether kindergarteners could grasp mathematics topics. A pretest-posttest-follow up design with two conditions. (Condition 1 educational kindergarten games on the computer, focusing on counting and comparison, Condition 2 educational kindergarten games on the computer, focusing on memory, counting and comparison) and one active control group (playing educational kindergarten games without mathematical content) was set up dealing with 45 preschoolers with a mean age of 68.78 months (SD = 4.46). Children were matched in kindergarten on their early mathematical and language skills as well as on their intelligence before the interventions took place. The study revealed that playing mathematical games in kindergarten had the potential to enhance the early mathematical skills. Children with initial weak mathematical skills in kindergarten caught up with their average performing peers, pointing to the importance of serious numerical games as "opportunities" in kindergarten. Both boys and girls benefitted, with a sustained effect in grade 1, revealing promising potential effects of offering opportunities to focus on mathematics even in very young children.