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exception in the past tense clauses sequence rule?

As all of us know as a general grammatical rule,the verb tense in second clause which comes after a simple past tense clause must be in one of the past tenses.

For example:

She knew she had made the right choice.

I touched the baby's head who was crying.

But I wondered when I saw this sentence.

I heard a little boy waving his hands above the water.

I saw a little boy drop his ice cream

Shouldn't it be:

I heard a little boy was waving his hands above the water?

I saw a little boy had dropped his ice cream.

Are there any exceptions to this grammar rule? If yes,what are those specific verbs ?