The answer is using big words but the concept is simple. Like talking about fractions as a quotient ring over a field.
A six year old can absolutely grasp that even means "being able to be split into two equally sized piles" where equally sized means each thing in the left pile can be matched to something in the right. 6 apples is even because you can split them into 3 and 3.
Then for infinity you separate them into the even and odd numbers, boom. Infinity is even.
Saying "infinity isn't a number", to me, is so much worse an answer because it's not satisfying. Because both you and the 6 year old know that isn't right. The 6 year old is grasping at a bigger concept but doesn't have the words.
A six year old can absolutely grasp that even means "being able to be split into two equally sized piles" where equally sized means each thing in the left pile can be matched to something in the right. 6 apples is even because you can split them into 3 and 3.
Then for infinity you separate them into the even and odd numbers, boom. Infinity is even.
Saying "infinity isn't a number", to me, is so much worse an answer because it's not satisfying. Because both you and the 6 year old know that isn't right. The 6 year old is grasping at a bigger concept but doesn't have the words.