Try making it a game, like this,
 It's a verb if you can use it after "you". For example, you walk, you walked, you run, you are, and (you) eat!
 It's a subject if it comes before the verb; if it's a noun, a name, a person, place, or thing. A noun is a single word. If you can add 'a/an/the' to it, it's probably a noun.
 It's an adjective if you can put it after the verb BE (is, am, are) and also before a noun, like this, The cat is fast. It's a fast cat.
 It's an adverb if it answers the questions Where, When, Why, What manner/How, like this.
At 7:00 p.m., Max ate his supper quickly because he had to work at the store.
When? => At 7:00 p.m.
How? => quickly
Where? => the store
Why? => because he had to work late at the store
Notes: Ask Who? and you get the subject or object of the sentence. Ask What kind of? and you get an adjective.
 It's a preposition if it's something a cat can do. For example, in, on, under, over, etc. Prepositions must take a noun as an object. For example, "under the bridge" is made up of a preposition and a noun phrase 'the bridge'. That noun phrase functions as the object of the preposition "under". The entire prepositional phrase "under the bridge" answers the question Where?, so it functions as an adverb (of place).
Note, every word in a sentence has a form, what it looks like, and a function, what it does. For example, the word "I" is a pronoun in form, and it functions as a subject in "I like pizza".
Note, every sentence has three basic elements: a subject, a verb, and an object. Note every sentence has a subject (e.g., imperatives: Eat your lunch!), and not every sentence has an object (e.g., I am sleeping).
 It's an object if you can replace it with what, like this,
I like pizza => I like what?
I slept under the bridge. => I slept under what?
When parsing a sentence, start by asking the 5Ws: who, what, where, when, why.
Hope that helps out some.