Sad, but it's misleading to call this a "farm" accident. There was no "farm" activity involved. The other thing about this is that it could have happened even if an adult was driving: hit a bump, toddler falls out and is hit by loader. Probably happened so fast, didn't matter what the driver's age was.
How many times have you operated machinery when something unexpected happens, takes you by surprise and it takes a second or so to react? Lot of damage can be done in that "second or so".
Just last week a 3 yrd old in Michigan was killed while riding in the ENCLOSED CAB of a combine his dad was operating. Kid leaned on the glass, it broke and he fell out. I'll bet if you asked 100 people they'd all say that the kid was in a safe place. Heck, I would have.
Not trying to say we should walk around in bubble wrap, there's risk in everyday life. But no sense in tempting fate by letting kids ride down the road in a loader bucket. Condolences to the families involved.