1. The -ing ending of verbs: he's running
2. The preposition in: It's in the box
3. The preposition on: It's on the table
4. The regular plural ending -s: cats and dogs
5. The irregular past tense form, such as went
6. The -s ending on nouns, which expresses possession: the boy's car
7. The full form of the verb to be, when it is the only verb in a sentence: Are they there? Is he ready?
8. The definite and indefinite articles
9. The regular past tense ending -ed: he jumped.
10. The regular ending for the 3rd person form if the verb, in the present tense -s: he walks
11. The irregular ending for the 3rd person form, as in he has/does
12. The full form of the verb to be, when it is an auxiliary verb in a sentence: are they running?
13. The shortened form of the verb to be, when it is the only verb in a sentence: he's ready, they're there
14. The shortened form of the verb to be when it is an auxiliary verb in a sentence: they're coming, he's going.
As for passive constructions according to David Crystal children get able to understand them rather late, closer to their 6-7 year.
Arina knows ONLY plural -s, though probably the prepositions as well. We've trained them a lot, but i'm not sure whether she remembers them or not.