Start reading blogs! They give you so many ideas.
I've found with kids as long as the meal itself doesn't look foreign or alien, and has a good taste, they'll hoe it down!
this particular blog is great because it's about 'vegan dad' who cookes for his wife and kids - most of the meals are easy (obviously) and he usually puts a note in about whether or not his kids enjoyed it!
http://vegandad.blogspot.com
Apart from that, as said above - the easiest way would be mock meats, although this could probably get expensive depending on your circumstances (ie. Single, multiple children, one party jobless, low income etc)
Quorn has a fun packaging and is pretty kid friendly, then you can accompany it with pretty average sides like peas and mash - at first anyway, after that just test their boundaries, and you will work out what they like and don't like