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.
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 ?