booking tickets

Hello,
I am using events manager 6.7.3. on some events I can offer two ot three types of tickets (ex adult and child) it works but I have a problem which is if you book only an adult ticket the child ticket is automatically 1 and it is not possible to enter a zero in the list choice . That is a real problem because all people do not need a child ticket!
Is there somebody who met this question and can help to solve IT ?

Thanks