When I first started building models as a kid, I started by following the directions, and never thinking outside the box. As I grew older, I began thinking of things that I thought would be cool, and started slowly making small one off changes to my models. Scratch building was the first venue I experimented with, trying to make Battletech inspired walkers for my growing 1/72 scale army. Tanks were cool, but I wanted walkers to trounce my dad's tanks (not that we played any games). Eventually my dad introduced me to Warhammer 40k when we went to England in 1999. He had been told about the game, and the miniatures line, and we stopped at a hobby shop in London (I think) and I got my first Space Marines. When we got back to the states, I looked GW up and found that they not only had really neat models (of powered armor- my boyhood dream) but encouraged their players and collectors to convert things. Then I discovered the bits catalog and the rest is history.
Today I rarely buy something the with intent of building it as it's meant to be built. I just assume that some changes will have to be made, and do so accordingly. This isn't to say that I convert everything, but I have my eye on what I can do to change things up if I think there is a need to change them. It generally runs something like, "Man, I need a sergeant model... Where's a power fist?" Sometimes it's a simple part swap. Sometimes I have to create a new part from components. Sometimes I have to do some really complex work to improve on a designed component. Whatever the alteration, for me it's what makes the hobby truly enjoyable. The ability to make what I WANT, and not necessarily what the designers intended. Converting things is freedom, and freedom is good.
I was driven as a youth to alter the models I had, and there are those who are the opposite. They don't really worry about what he designers intended, and just go with it. That's cool too. But there are those who would like to alter what they have, but get worried about messing it up. I know because I can be like that. You have an idea and the execution of that idea is, for all intents and purposes, beyond your current reach. This is a good thing as it means that as a hobbyist you are stretching your skills and learning new things. Doing complex conversions is a way of building confidence by putting yourself into a very cheap (relatively speaking) fire. Mess up- you're out the money for the model. Land it, and you've got a really awesome model that people will compliment you on. It's an "either or" proposition that forces one to think of a plan, and execute on that plan, potentially pushing the envelope on their abilities and learning something new.
This is why converting models is so damned amazing. It's not just about making really neat toys to play with in the table top, but about developing the ability to visualize something and make it a reality. It's a life skill wrapped up as a game. There are plenty of ways for one to develop those skills and abilities, but few are as cheap or capable of producing instant satisfaction as converting minis. Add to that the artistic component and you have a means of teaching a child skills that they will carry with them for a lifetime. The ability to see potential, and the artistic capacity to see it through.
It's not something that parents think about. They see the price tag on some of the models that their kids want, and squirm at the notion of buying some plastic thing that holds, to them, zero value. But the value isn't in the model itself, it's in the expression that model can allow, and the excitement that the model brings with it. Not every child likes the same things- my daughter likes to draw and paint, my son likes to build. That difference in the child is what matters. It's what mattered to me and my sister. She got into D&D because of the narrative nature of character creation- I followed Warhammer because of the models and the ability to BUILD what I wanted. I developed a narrative desire as I moved forward, but that narrative desire was built on the plastic models I built. Everything I do with this blog, and the stories and posts I write started with my dad getting me models as a kid, and letting me make mistakes, break things, and probably get a little high in my room off of Testors while building all those failed models.
Converting can be the opening to a grand adventure within the mind for some kids. Kids like me. Perhaps kids like yours- maybe even the reader themselves. The cost is worth it. The cut fingers, the screwed up models, the plastic chunks littering the floor. It's a process, and a learning adventure that can open the doers mind in ways that school never will. Free flowing learning, the kind that drives an entrepreneurial spirit, and the willingness (even if not really understood) to risk failure for something greater. It's small- but the road to success in life is built on the tops of small endeavors. So encourage your kids and allow yourself to convert things, to go against the instruction booklet and make something new and original. Freedom is down that path. And we all know, freedom is good.