Locate the participle (not the entire participial phrase) and the word it modifies. Reminding the younger children to walk carefully, the guide led the group into the cave.
Participle:
V
Modified:

Reminding, younger and carefully.

Explanation:

A participle is word that is derived from a verb by the addition of -ing. At the same time, it can also act as an adjective in a sentence. For example, running or cunning in a sentence is a participle while sparkling water or cunning fox is also a participle which acts as an adjective.A word or phrase that modifies another word either a noun or a verb in a sentence is simply called a modifier. In case of a noun, adjectives are used as modifiers such as blue pen, pink dress, eldest son, etc, while in case of a verb, adverbs are used as modifiers such as talk clearly, jump swiftly, smile gently,etc.Here, the word "reminding" is the participle while "younger"and "carefully" are the modifiers.

What is the topic of the paragraph? and what section? if you could include the text that would be great! you!