Perhaps the simplest  tune  with the most repetitive    wording,  though not quite so slow, is

"Turn, Turn, Turn". 

https://www.youtube.com/watch?v=2zx6j4vI8lE (with lyrics)

TURN TURN TURN by The Byrds

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To everything - turn, turn, turn
There is a season - turn, turn, turn
And a time for every purpose under heaven

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A time to be born, a time to die
A time to plant, a time to reap
A time to kill, a time to heal
A time to laugh, a time to weep

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To everything - turn, turn, turn
There is a season - turn, turn, turn
And a time for every purpose under heaven

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A time to build up, a time to break down
A time to dance, a time to mourn
A time to cast away stones
A time to gather stones together

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To everything - turn, turn, turn
There is a season - turn, turn, turn
And a time for every purpose under heaven

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A time of war, a time of peace
A time of love, a time of hate
A time you may embrace
A time to refrain from embracing

Most children's songs are very easy songs with repetetive words~~~~~

Hello Smelval:

   Here is a link to a list of "slow"   songs that make for an excellent study material.

http://www.italki.com/entry/454515

   They lyrics to all of these  songs can be found in my Notebook Entries.

    Also, you can just do a websearch using the song title like this:    "Song Title" +  lyrics

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Wow there are so many. It depends what you want to learn,