Biggest and Smallest

I bought some books for Lucas, preparing for his school holidays. He was so excited, he started reading the books and doing the exercises. Then, one of the exercise is circle the biggest number (from a list of 4 numbers) and cross the smallest number (from a list of another 4 numbers). He doesn't understand the meaning of biggest and smallest number. I tried to explain by saying 'If you count from 1, the biggest number will be the number you reached last. The smallest number is the number you reached first'. He doesn't get the explanation and got most of the exercise wrong.

Later that night, I asked Dominic if he has better explanation. He said the same thing as me:( Now, we have to think harder on how to explain the concept to him. Is this the beginning of a more difficult explanations to come? If he learns new concept from me, I am very happy that I can 'educate' him. It's the parents' job and not tuition teachers' job, right?