(3Po has had a bad cold and cough for the past several days)
3Po: Mama, why am I sick?
Me: Because there are germs inside your body that are attacking your body, and they are making you sick.
3Po: But aren't the white blood cells supposed to fight the germs?
Me: Yes, but sometimes your body is not strong enough to fight the germs.
3Po: Why isn't my body strong enough?
Me: Well, maybe it's because you aren't eating enough healthy foods. Or maybe it's because you are staying too late and your body isn't getting enough rest. Or maybe it isn't your body's fault. Sometimes there are germs that are so strong that your body cannot fight them.
3Po: Yeah, there are germs like Amazo(note: Amazo is an all-powerful robot who frequently battles the Justice League, i.e. Superman, Batman and their superfriends). No-one can beat Amazo
Me: But the Justice League can beat Amazo, right?
3Po: Yeah, the Justice League can beat Amazo. The Justice League should get into my body to fight the germs there!