Each day you play the game you will get a stamp. Collect the indicated number of stamps to unlock the corresponding mini-game:

Number order memorization: 1 stamp
Syllable counting: 2 stamps
People counting: 3 stamps
Learning tips: 5 stamps
Change your stamp design: 7 stamps
People counting (hard version): 9 stamps
Math 100 (hard version): 11 stamps
Multi-step mental math: 13 stamps
Clock reading: 15 stamps
Multi-step mental math (hard version): 17 stamps
Verbal math: 20 stamps