Learn Russian: Это самое опасное место для заблудившихся детей. - This is the most dangerous place for lost children.

To form the active past participle, take the infinitive заблудиться (to get lost), drop the -ть, and add the suffix -вш-. Then add the adjective ending (here, -их for the plural) and put the reflexive particle -ся at the very end.

Why is the ending -их- used inside заблудившихся?

Participles behave like adjectives and must match the noun they modify in case, number, and gender. The preposition для requires the genitive case, so дети (children) becomes детей (genitive plural). The participle matches it with the genitive plural adjective ending -их, which is placed right before the reflexive -ся.

Is the reflexive particle always -ся at the end of a participle, even if the case ending finishes with a vowel?

Yes! Unlike regular verbs which switch to -сь after vowels, reflexive participles always use -ся at the very end, regardless of whether the adjective ending before it ends in a vowel or a consonant. Here it follows the consonant х, but it would still be -ся even after a vowel.

Why do we use самое with опасное место?