Learn Spanish (Spain): Quiero que el niño friegue la vajilla hoy.

Fregar is a stem-changing verb where the e changes to ie. Just like in the present indicative (él friega), this stem change carries over into the present subjunctive for the yo, tú, él/ella/usted, and ellos/ellas/ustedes forms.

Why is there a "u" in friegue? Shouldn't it be friege?

The infinitive is fregar, which has a hard "g" sound (like in "go"). In Spanish, a g followed by an e makes a soft, breathy sound (like the "h" in "hello"). To keep the original hard "g" sound when we add the subjunctive -e ending, we have to insert a u, making it friegue.

Why do we need the subjunctive mood (friegue) here instead of the indicative (friega)?

The phrase quiero que (I want that...) expresses a desire or attempts to influence someone else's actions. When you have a verb of wishing followed by que and a new subject (changing from "I" to el niño), the second verb must be in the subjunctive.

In Spain, is it more common to use fregar or lavar for washing dishes?

In Spain, it is very common to use fregar (which means "to scrub" or "to mop") for washing dishes, often seen as fregar los platos or fregar la vajilla. While lavar is understood perfectly, it is much more commonly used for dishes in Latin America.