Diminutives in Spanish are those -(c)ito/a endings that you put on words to minimize them in some way. People mainly use diminutives to show affection or to make something smaller or cuter. English has the -y ending, but it's not as productive as the Spanish -(c)ito/a.
Here are all the different ways you can express the same diminutive sentiments, but in English.
To Show Affection
Amorcito corazón
Yo tengo tentación
De un beso
Every language needs a way to show affection. You're probably used to using the diminutive in Spanish, like in the oh-so-famous Pedro Infante song that we referenced just now.
So how do you express affection in English?
To show affection for significant others, English speakers generally rely on pet names, like baby, boo, baby boo, babe, and even shmoopy (seriously). For platonic affection, pet names like dear, darlin', honey, and sweetie are generally okay and don't cross any social boundaries.
Then again, saying anything with the wrong intentions may cross a boundary or two. We're looking at you, cat-callers.
In addition to pet names, adding -y to nouns and names often works. A doll becomes a dolly, a dog becomes a doggy, and a horse becomes a horsey. This doesn't always work, though: sometimes, if a word already ends in a vowel—especially a long "e" sound—adding -y doesn't sound right. Adding -y to a long word also doesn't work.
Who knew big nouns couldn't sound cute?
As always, listen and learn. Some terms of endearment might be okay for some relationships and some people, but might sound weird in your particular situation.
To Reduce Size
A dog in Spanish is un perro. A puppy in Spanish is un perrito. A cup of water is un vaso de agua. A small cup of water is un vasito de agua, which you can also use if you want to playfully or nicely request a cup of water.
As you may have discovered already, English doesn't have a consistent way to express small-ness. There are certain words used for younger animals, and "little" or "bit" can often be used to express a small quantity of something.
To Minimize a Situation
In Spanish, you might use the diminutive to be playful, to sound sheepish, or to not come off as super bossy or serious.
What does English have that you can use, you ask?
Hehe. Nothing, really. But to minimize situations in English, use filler words like "just," "a little," "a bit," or "kind of." Here are some examples:
Playful: To sound lighthearted, playful, and not too serious, use contractions and words like "kinda" and "sorta." This might make you sound wishy-washy and indecisive, but it helps if you want to sound less commanding. For example: "I kind of don't want to go" instead of "I don't want to go" sounds way less intense.
Not bossy (friendly): Use questions and contractions. In some dialects of English, the speaker asks if the person wants to do something instead of asking them if they can. For example: "Wanna hand me that spatula?" This is literally asking if the person wants to do something, but it's essentially (and politely) telling them to do it. This is even lighter than asking, "Can you hand me that spatula?"
As always, the most important thing is to listen to the way people express these sentiments in movies, TV shows, books, and in real-life conversations. But you can use flashcards if you want.