In the middle ages how did children of all social classes think about when they looked at knights?

[old lady]

Very few young men (and NO young women) became knights. In order to aspire to knighthood, your father had to be of noble blood and he had to have enough money to equip you - that armour wasn't cheap, nor were the horses.
Mostly children of the lower classes never even saw the knights when they were all kitted out, because they didn't parade around the streets, they wore their armour for tournaments and the lower classes were not invited to the tournaments. Nor were the middle classes. So the only children who would even see the knights were the children of the nobility and the royalty - and they just regarded them as part of the scenery. Nothing special. Again, very few children outside of the nobility would have even seen weapons. They weren't on parade, as modern militia is.