I don't understand this passage. I believe in pre-trib but if there is pre-trib why does Isaiah 13: 16 mention children during the last days?

"Their children also will be dashed to pieces before their eyes; their houses will be plundered and their wives ravished"

This site takes the same position that I believe, which is that both an ancient and a future application of prophecy are in view.

http://www.wordexplain.com/Isaiah_13_and_the_Day_of_the_LORD.html

Fair Use For Educational and Discussion Purposes

Isaiah 13 is a prophecy which exemplifies a dual fulfillment of the Day of the LORD. One of those fulfillments was a historical fulfillment. This prophecy was fulfilled in history when the Medes conquered Babylon (Isaiah 13:1-5, 17-22). But there will also be an eschatological fulfillment of this prophecy. Isaiah uses language so global, so extensive, and so cosmic in scope that it can only refer ultimately to the unprecedented devastation with which God will afflict the world during the Tribulation. 

But to answer the original question about children in the Tribulation, we can also refer to this verse:

How dreadful it will be in those days for pregnant women and nursing mothers! There will be great distress in the land and wrath against this people.  Luke 21:23

Whatever happens at the rapture, we are certain children will still be conceived and born afterward, as this takes place 42 months later.

Boricua, first, welcome to the RITA Now family! We're glad you decided to join us!

The children spoken of in Isaiah, are the children who will be born here during the tribulation. After the rapture, women will give birth during that 7 years. The scripture in Isaiah goes along with the scriptures in Matthew 24 which take during the middle of the tribulation and onward beginning when the a/c stands in the temple declaring himself to be God. The children and people who have given their hearts to Jesus will be killed, tortured, etc for their faith. Their homes will be ransacked, and they will have to flee into the wilderness to escape persecution.

I hope that helps!

Matthew 24:9-22

Then you will be handed over to be persecuted and put to death, and you will be hated by all nations because of me. At that time many will turn away from the faith and will betray and hate each other, and many false prophets will appear and deceive many people. Because of the increase of wickedness, the love of most will grow cold, but he who stands firm to the end will be saved. And this gospel of the kingdom will be preached in the whole world as a testimony to all nations, and then the end will come.

“So when you see standing in the holy place ‘the abomination that causes desolation,’ spoken of through the prophet Daniel—let the reader understand— then let those who are in Judea flee to the mountains. Let no one on the roof of his house go down to take anything out of the house. Let no one in the field go back to get his cloak. How dreadful it will be in those days for pregnant women and nursing mothers! Pray that your flight will not take place in winter or on the Sabbath. For then there will be great distress, unequaled from the beginning of the world until now—and never to be equaled again. If those days had not been cut short, no one would survive, but for the sake of the elect those days will be shortened.

God Bless and Love,

FW