Learn Swedish: Snälla barn hjälper alltid.

It can! When used to make a request, it translates to "please". But it is actually a form of the adjective snäll, which means "kind" or "nice". In this sentence, it is used as a regular adjective describing the children.

Why does the adjective snälla end in an -a?

Because it is describing a plural noun. The basic adjective is snäll, but we add an -a when describing plural nouns (like children) or definite nouns.

How can we tell barn is plural here if it looks exactly the same as the singular word for "child"?

In Swedish, ett-words that end in a consonant (like ett barn) do not change in the indefinite plural. We can tell it means "children" here because of the plural adjective snälla. If it were singular, it would be ett snällt barn.

Why is the word order hjälper alltid instead of alltid hjälper like in English?

Swedish strictly follows the V2 rule in main sentences, meaning the verb must be the second piece of information. The subject (Snälla barn) takes up the first position, so the verb (hjälper) must come next. Adverbs like alltid (always) are then placed right after the verb.