I heard this from a small boy the other day.

Problem:
The word “ones” is unnecessary in this phrase.

Explanation:
The boy said a sentence such as “These ones are bigger.”

The word “these” in the phrase “These ones …” is acting as a determiner.

Other examples of “these” as a determiner include:

• “I like these chocolates.”
• “Do you want these tickets?”
• “He should give her these flowers.”

Also, it is possible to pluralize the singular numerical pronoun “one”, as in the following examples:

• “I like the vanilla ones.”
• “The ones in green are tickets for the front row.”
• “Are the pink flowers the ones that he wants?”

However, when the word “ones” is preceded by a plural determiner (such as “these”), it is best to drop the word “ones”, thereby converting the determiner “these” into a demonstrative pronoun, as shown in the following examples:

• “I like these.”
• “Do you want these?”
• “He should give her these.”

Solution:
“These …”