All guns are dangerous or safe depending on how you use them. It is much better to gun proof your children rather than trying to childproof your guns.
Your decision to take the safety course is obviousely a good idea. Try to be even safer than the experts. Be an absolute fanatic on safety, but still keep the gun where it will be available quickly when needed.
I wouldn't recommend a really powerful gun like a .357 mag or .44 mag in the house as the blast is terrible, deafening and penetration is often too great. Maybe a .38 special with full wadcutter target loads.
A shotgun is great except even short ones are a little hard to handle indoors.