@pastanaga - I think people get a bit worried about having their kids work with pumpkins unsupervised, just because it can be dangerous. If the children are too young, a good alternative might be to provide safety scissors and some pre-made pumpkin cutouts so they can design and cut out their own face and maybe even make it into a mask.
There are a lot of great Halloween games for children, but do remember to be sensitive to some of the issues that surround the holiday. Many people might be offended at depictions of witches, for example, as they can be a reminder of past atrocities. It's also important to make sure people don't wear costumes that stereotype others. If you're going to have a theme, make it a good one. Something like "Cowboys and Indians" is just asking for trouble.