Learn Swedish: Barnen sa tack för maten. - The children said thank you for the meal.

Barn (child) is an ett word that ends in a consonant, so its plural form doesn't change: one child is ett barn and children is barn. To say "the children" in the definite plural, you add the ending -en to get barnen.

Is sa an irregular verb form?

Yes, it is the past tense of säga (to say). The present tense is säger and the past tense is sa. You might occasionally see it spelled as sade in older or formal texts, but sa is how it is pronounced and usually written today.

Is tack för maten a common phrase in Sweden?

Very common! It literally means "thanks for the food," but it is the standard, expected way to say "thank you for the meal." In Sweden, it is an important part of polite etiquette to say this to whoever cooked the meal when you are finished eating or leaving the table.

Why does the translation say "the meal" when maten usually means "the food"?

The Swedish word maten literally translates to "the food." However, because tack för maten is a fixed cultural phrase used exactly where English speakers would say "thank you for the meal," that is the most natural translation.