In Shema, the common way I have seen children taught is “vi-aHAvta”. The correct way is “VI-ahavTA”. There is a difference in meaning between the two, and I was told one is not yotzei if one reads it the wrong way.
The common way of singing Adol Olam and Yigdal also have many mistaken emphases.
For example, “nosein larasha ra, kirishaso” should really be “nosein larasha, ra kirishaso”. Translated, “…He gives to the bad wicked one, like his wickedness” is incorrect. It should be (forgive the rough translation) “…He gives to the wicked one, ‘bad’ like his wickedness”.
And many others if you simply listen as they are sung.
Not to mention that the whole havara of many of these tunes including the ones for Anim Zemiros is almost completely incorrect as the songs typically emphasize the first syllable as is typical of American English instead of the last syllable of lihavdil Lashon Hakodesh; often, the meaning is changed and is still incorrect regardless of whether or not it actually changes the meaning of each word.
Someone’s got to redo all these tunes.