I'm likely late to the game on this one, but I have stumbled upon the best tool for cutting the top off of your pumpkin. A hacksaw blade! Either start with a standard knife to make a slit and then insert the blade, or push the blade through. Then just saw away, being sure to choke up on the blade and ensure you keep your inward angle. It also makes cutting your registration notch a cinch. No more sketchy kitchen knives that get stuck in the pumpkin, as the hacksaw blade just slips along as you cut. I used one intended for cutting metal, so the teeth were very close together. You're less likely to cut yourself than with perhaps the more spaced/larger tooth blades. I'd hazard that children could use it safely as well.
I've also found that rubber gloves (I really like the Ammex nitrile) are a great way to prevent the pumpkin under the fingernails and itchy drying pumpkin on the hands and wrists. I've seen some people wear light work gloves when cutting their pumpkins to reduce the possibility of cutting your supporting hands. Seems like a good idea.
This is my 3rd attempt over the years to sculpt-carve a pumpkin. I'm getting better, but I've got a way to go before I'm satisfied with the results. Carving (a subtractive process) is tricky!!
The pumpkin shown was for a friend, who is a den mother in the Cub Scouts. It's to be 1st prize for a costume contest. I hope it's good enough to satisfy an 8 year old at least!