Select the most appropriate option to fill in the blank.

We saw some children ______ with one another as we were walking around.

quarrelling

The most appropriate option to fill in the blank is quarreling.

The sentence is about the children who were quarreling with one another. The word "quarreling" is the present participle of the verb "to quarrel", which means to argue or disagree in a noisy way. In this context, the speaker is saying that the children were arguing or disagreeing in a noisy way as they were walking around.

The other options are not as appropriate.

• Quarrels is the plural form of the noun "quarrel", which means an argument or disagreement. This is not the most appropriate option because it does not indicate that the quarrel was happening at the time the speaker saw the children.
• Quarrelled is the past tense of the verb "to quarrel". This is not the most appropriate option because it does not indicate that the quarrel was happening at the time the speaker saw the children.
• To quarrel is the infinitive form of the verb "to quarrel". This is not the most appropriate option because it does not indicate that the quarrel was happening at the time the speaker saw the children.