Text message archive?
Depending on what you need to use it for and if you have a Mac or PC, there are multiple solutions:

On a Mac: for example use http://www.ecamm.com/mac/phoneview/, can also Google for alternatives

On a PC: the PC counterpart is http://www.copytrans.net/download.php

Since you mention your ex and your son, you might need these for legal purposes (hope not for you!).
In this case screenshots might be your best bet, as your lawyer might want to see those if things get rough (still your iPhone will be the best resource, so don't delete them there):
Scroll to the top of the messages you need


If timestamps are of value, swipe in from right side of screen to
show them
Press the power button (top right of iPhone) and the Home button
at the same time for ~1.5 secs and release
Scroll down so the last sentence which you just screenshotted is
shown at the top (thus the order of messages can easily be deducted)
Repeat steps 2 and 3 as often as needed


Good luck!