* You - This is a pronoun, not a noun.
* Must - This is a verb.
* Give - This is a verb.
* A - This is an article, not a noun.
* Day - This is a noun (referring to a period of 24 hours).
* Card - This is a noun (referring to a piece of paper).
* To - This is a preposition.
* Every - This is a determiner, not a noun.
* Child - This is a noun (referring to a young person).
* Class - This is a noun (referring to a group of students).
Therefore, there are 4 nouns in the sentence: day, card, child, class.