iPad messaging with multiple family iPads
If all you care about is having your kids text message only people who have Apple devices signed into an Apple account using iCloud, then the process is pretty straightforward.  You go to the settings on the iPads and then head over to Messages -> Send &amp; Receive.  On this page you can add whatever email addresses you've made up for your kids and then confirm with your Apple ID.  Their email will be sent a confirmation with a link that needs to be clicked.  Now you can set their Send &amp; Receive to only have that address checked for "You can be reached by iMessage at" and for "Start new conversations from".

The actual texting to/from any number capable of text messaging is only going to function within the context of your iPhone's ability (i.e. your phone number).  You can either enable or disable that feature for each specific device(iPad), or if they are data capable devices (not the WIFI only version, but rather 4G/LTE) then maybe the provider will be able to set them up a phone number for texting (I'm not 100% sure on that so check with them first).

Basically, even though Apple devices can all be set up using specific addresses to send/receive messages from, they really can't send from one single data/texting package and route only between specific devices based on some other hidden meta data (meta data which is impossible to exist within a text message btw).

So let me try to make it simpler.  You can allow for the iPads (say WIFI-only) to send/receive text messages by way of the Text Message Forwarding feature, yet it will always appear on your iPhone because ultimately that's where messages are delivered from/to.  If your iPads message someone in the Apple ecosystem (i.e. has an Apple ID) then the individual address you set up on those iPads for Messages -> Send &amp; Receive can be used.  This is strictly limited however to Apple IDs or addresses associated with one.