Learn Finnish: Lapset juoksevat talon ympäri. - The children run around the house.

In Finnish, words like ympäri (around) are usually postpositions. This means they come after the noun they relate to, unlike English prepositions which come before. Most postpositions require the noun before them to be in the genitive case, which adds an -n to the end. So, you must say talon ympäri (literally: house's around).

Why is the verb juoksevat so different from its dictionary form juosta?

Juosta (to run) belongs to a group of verbs that often trick beginners. When you conjugate it, the ending -sta drops off and an -e- is added. Also, a consonant change happens where the s becomes ks. That gives us the stem juokse-. Finally, you add the ending for they (-vat) to get juoksevat.

How does lapsi (child) become lapset (children)?

To make a basic noun plural, you add a -t to the end. However, many older Finnish words ending in -i, like lapsi, change that -i to an -e- before you add plural endings. Therefore, lapsi plus -t becomes lapset.

Why does the verb end in -vat instead of -vät?