Difference in altitude
The Zugspitze is almost 3000m above sea level and that alone can be a very difficult experience for small children. In addition to the altitude the Tiroler Zugspitzbahn travels up the mountain in just 10 Minutes, transcending an altitude of 1.750 Meters. The air at this level is much thinner which puts more pressure on our bodies. Children should drink plenty and also eat and then there will be no problems!
During the cable car ride(most frequently on the ride down the mountain) children can complain of "ear ache". Small children are unable to control the pressure on their ears created by such a rapid change in altitude. Giving them a sweet or something to drink will definitely help! The pressure eases very soon after you arrive back in the valley.