When you are cutting holes into parts you'll need to use a sharp knife. By their very nature, sharp knives are dangerous. Be careful. Cover the blades when not in use and always store the knife where it won't get knocked and fall onto someones foot.
Make sure you have plenty of spare blades for your knife as paper is surprisingly abrasive and your blades will soon loose their edge. X-acto and Swan Morton both make excellent craft knives.
I use Swan Morton standard scalpel handles and 10A blades both of which I buy from eBay. They are generally very reasonably priced.