Twelve bright picture cards, and under each one two words: the singular and the plural. A child counts what is in the picture, one hat or three apples, and circles the word that fits.
It is the gentlest way into singular and plural nouns, because the only question is “one or more?” Nothing needs to be written, so a child who is still slow with a pencil can focus entirely on the idea.
A few cards use es (fox, dish, box), which gets a first look at the longer ending before a child has to spell it themselves. The pair of socks is a nice one to talk about, since two things that go together still make a plural.