I almost didnt respond to this thread as I don't want anyone to think I was passing judgement or be pretentious enough to tell someone else what to do with their baby. That said, I decided it wasn't fair to omit my opinion either as the OP asked an honest and earnest question.
That said, a long time ago, we had to make a decision with the tractors we were restoring.
We were restoring my Grandpa's TO 20, My Dad' MH 50, and my MH81 and we had witnessed people who would literally scream at children who dared to touch a tire, let alone be so bold as to ask to sit on their tractors.
My parents and I decided we were in the hobby to share what we had. To show people how it used to be done or the tractor Dad grew up driving. We decided that there would never be a tractor to shiny for a little kid to sit on supervised. We knew that if we got a scratch on one, we would feel bad... But it was worth the price to see the hundreds of smiles.
I have been involved with tractor shows for over 20 years, and in those years I have cherished the memories of a little upturned face listening to me, my parents, their parents as they hear the tale of what this wonderful piece of equipment used to do and how it helped make this country what it is today... Then you can see the shyness creep in... They want to ask, but they can't be that bold... The look of amazement when you ask them if they want to sit on your tractor. Priceless.
Some of my favorite pictures from shows were of friends, family, and strangers kids sitting on my 81 or one of the others and just grinning.
Do they all look like the day we painted them? Of course not. But each little mark, be it kid caused or from actual use is a badge of honor and I'm proud they have these imperfections.
And now I couldn't be prouder of my Children as they are starting to do the same. They offer to let little ones sit on them and my son seems to have my gift for gab, as I have witnessed more than one youngster getting schooled on the benefits of owning a MF10.
Everyone needs to decide for themselves, its a personal decision that cant be made by anyone else, but for me and my family, we love the fact that we can share the stories and the more keisters that sit on our tin pan seats, the better.