Learn Finnish: Jos lapsonen itkee, soita minulle. - If the dear child cries, call me.

The suffix -nen acts as a diminutive. It doesn't just mean "small"; it often adds a strong tone of affection, endearment, or fragility. While lapsi is just "child", lapsonen conveys "dear child" or "sweet little child".

The base word is lapsi, so why is there an o in lapsonen instead of it being lapsinen?

When adding the diminutive -nen suffix, the stem of the noun sometimes alters to fit traditional phonetic patterns. For several older words ending in -i, an -o- or -u- replaces the final vowel of the stem. Therefore, lapsi becomes the highly lexicalized form lapsonen.

Why is the imperative soita used in a jos (if) sentence instead of a conditional verb?

The jos clause sets up a real, likely condition ("If the child cries"). The main clause gives a direct, real-world command of what to do in that situation ("call me!"). Therefore, the regular imperative soita is correct. You would only use the conditional (like soittaisit) if the whole situation was hypothetical.

I remember soittaa can also mean "to play an instrument". Why does it take the allative case minulle here?