...and it is not directly related... but
My sisters co-worker told her this.
This happened last fall on a farm in Michigan owned by the family of my sisters co-worker, they were her relatives.
Her well meaning father in law took 2 of his other grandsons for a ride on his tractor ..and had the boys in the front bucket while driving around slowly. He apparently wasn't paying close enough attention and the smallest boy bounced out and was run over by the large rear tractor tire... and was crushed to death instantly.
My first reaction is that grandpa just wasn't very smart.. and it is certainly totally his fault.. but the bad feelings that will stay with him (and the rest of the family) till the day he dies must be just unbearable.
On the other hand.. bad accidents happen to good people all the time.. for no good reason.. and you can't live in a padded cell so that you are safe all the time.
If you do it strap him in good and get a helmet for him and ride where there is no traffic.