Have you seen DucDuc's The Table? It's kind of...brilliant. Individual panels can be turned over for white board scribbling while your kids are patiently (or not patiently) waiting for dinner to be served.
Or, if you're serving a more sophisticated set, simply turn the white board panels over for the all walnut look.
One end of the table even features an imperceptible slit to roll out drawing paper across the table.
Not interested in shelling out the $3K+ "The Table" pricetag for your kids dining entertainment? Paper Source offers these disposable placemats with step by step doodle instructions.
If your kids' medium of choice is chalk, these are fun too...
Or, another novel idea... just tell your kids to sit there and eat!