The disciples didn't really ask silly questions, we just don't understand where they are coming from because we are not brought up Jewish. I suppose this instance would go all the way back to Deuteronomy 28 where, as part of the covenant (with Israel, not gentiles) God promised that if they followed him they would be blessed with easy lives (good crops and livestock, peace with enemies, healthy family, etc.) but if they fell away, the opposite. You pretty much need to read the whole chapter, but vv 1-14 outlines the blessings, vv 15-26 outlines the curses.
I don't have the references but I also think there are verses which talk about curses to certain sinners that fall to them and/or following generations. (Solomon comes to mind, he was not a good king, but 'for the sake of his father, David' his kingdom was taken away only after Solomon died).
So I think there question is reasonable. And as Jesus replies, this one was not due to anyone's sin but for the glorification of God.
Deu 28:1 And it will be, if you shall listen carefully to the voice of Jehovah your God, to observe and to do all His commandments which I command you today, Jehovah your God will set you on high above all nations of the earth.
Deu 28:2 And all these blessings shall come on you and overtake you, if you will listen to the voice of Jehovah your God.
Deu 28:3 You shall be blessed in the city, and be blessed in the field.
Deu 28:4 The fruit of your body shall be blessed, and the fruit of your ground, and the fruit of your cattle, the increase of your cows, and the flocks of your sheep.
Deu 28:5 Your basket and your store shall be blessed.
Deu 28:6 You shall be blessed when you come in, and blessed when you go out.
..and so on.
Deu 28:15 And it shall be, if you will not listen to the voice of Jehovah your God, to observe and to do all His commandments and His statutes which I command you today, all these curses shall come on you and overtake you.
Deu 28:16 You shall be cursed in the city, and cursed in the field.
Deu 28:17 Your basket and your store shall be cursed.
Deu 28:18 The fruit of your body shall be cursed, and the fruit of your land, the increase of your cows, and the flocks of your sheep.
Deu 28:19 You shall be cursed when you come in, and cursed when you go out.
..and so on - it gets pretty rough.
including..
Deu 28:28 Jehovah shall strike you with madness and blindness, and astonishment of heart.
Deu 28:59 then Jehovah will make your plagues remarkable, and the plagues of your seed great and persistent plagues; with evil and long-lasting sicknesses.
Deu 28:61 Also, every sickness and every plague which is not written in the book of this Law, Jehovah will bring them on you until you are destroyed.