Who are the mother's of Salem in the Bible?

There is only mention of the king of Salem in The Bible, nothing about the mothers or any other citizens. You are probably thinking of the children's hymn:

When mothers of Salem their children brought to Jesus,

The stern disciples drove them back and bade them to depart:

But Jesus saw them ere they fled and sweetly smiled and kindly said,

"Suffer little children to come unto Me."

"For I will receive them and fold them to My bosom:

I'll be a shepherd to these lambs, O drive them not away;

For if their hearts to Me they give, they shall with Me in glory live:

Suffer little children to come unto Me."

How kind was our Savior to bid these children welcome!

But there are many thousands who have never heard His Name;

The Bible they have never read, they know not that the Savior said,

"Suffer little children to come unto Me."

O soon may the heathen of every tribe and nation

Fulfill Thy blessèd Word and cast their idols all away!

O shine upon them from above and show Thyself a God of love,

Teach the little children to come unto Thee!