Psalm 

"My strength is dried up like a potsherd, and my tongue sticks to my jaws; you lay me in the dust of death," (Psalm 22:15 ESV).

A potsherd is a piece of a very old pot. The Meaning is rather self-evident, the servant's strength is so weak that it is like a potsherd: "his strength was not vigorous like a green tree that was growing, and that was full of sap, but it was like a brittle piece of earthenware, so dry and fragile that it could be easily crumbled to pieces," (Barnes).

The passage continues, stating his tongue stuck to his jaws. This is to say he thirsted greatly: "An extreme and agonizing thirst sets in - the secretions generally fail - and the saliva especially is suppressed, so that the mouth feels parched and dry," (Pulpit Commentary).

Barnes reiterates this point noting: "The meaning here is, that his mouth was dry, and he could not speak. His tongue adhered to the roof of his mouth so that he could not use it," (Barnes).

Laying in dust or on the ground is a metaphorical statement as if to say he was on the verge of death, similar to the soldier who lays on the field (Barnes).

"Blessed shall he be who takes your little ones and dashes them against the rock!" (Psalm 137:9).

To say the least, this verse looks bad, and in all honesty, the actual meaning is better, but not exactly nice... So, let us look over it. To get a full context of this story, let us read the entire chapter. It is only nine verses so don't worry. "...There we sat down and wept, When we remembered Zion. Upon the willows in the midst of it we hung our harps. For there our captors demanded of us songs, and our tormentors, jubilation, saying, “Sing for us one of the songs of Zion!” How can we sing the Lord’s song In a foreign land? If I forget you, Jerusalem, May my right hand forget its skill. May my tongue cling to the roof of my mouth If I do not remember you, If I do not exalt Jerusalem Above my chief joy...you devastated one, Blessed will be one who repays you...Blessed will be one who seizes and dashes your children Against the rock." (Psalm 137:1-9). 

So we read in the passage that the ones who write this passage are under capture. Before anything is started, it should be noted that God hasn't said anything in this chapter, so one can't claim God is evil because he endorses child murder.  We read at the end, "blessed will be one who repays you." (Psalm 137:8).  The Jews, very clearly are the ones saying this, but why? Well, as the verse says, "...repays you..." (Psalm 137:8). The Jews want revenge for being held captured and tortured. To be fair, they definitely could have said it more lightly, but I feel most people after being tortured would be losing it a bit.