Lots of good suggestions, but prepare now!
Okay, there are a lot of good suggestions here, however other than closing the garage door, I see nothing that talks of security before the fact.
Most local police departments will come to your house and give you a security assessment. Some things will include:
1. ALWAYS close and lock all doors. Locks should be sturdy and well installed. Lock the door from the garage to the house with a sturdy lock!
2. Keep windows locked. If you keep them open for ventilation, open them just enough for air circulation and have a positive stop to prevent unauthorized opening and entry from the outside.
3. Use security film on windows to prevent the "rock" entry method.
4. Use lighting to keep areas around the house and garage visible.
5. Remove shrubs and other plants from around windows and doors if they offer a hiding place for anyone trying to break in or ambush you.
6. Install solid wood or steel doors as the typical hollow core doors used in most construction are easy to breach.
7. Get a good dog for security. Small dogs that are rated as good watchdogs (not guarddogs) are Yorkshire Terriers and West Highland White terriers. I have both and they let me know when the neighbors four houses away open their car doors! For large dogs, retrievers and shepherds are good. These large dogs are good for outside as well. The small dogs are called coyote bait if they are outside at night and Eagle food during the day!
8. Have a family response plan, and practice it, for possible scenarios of burglary, invasion, fire, flood, earthquake, etc.
This is just a start; however with before-the-fact security you become a hard target and the BG will probably go elsewhere thus minimizing your need for arms. However, an 870 or 357 is a good line of defense if other security measures are breached.
By approaching your family with this type of security plan in mind, you can do a lot without even mentioning arms for defensive purposes. Also, research the types of crimes against residences in your local area so you can show the family that it can, and does happen in your neighborhood!
Finally, as others have stated, don't bother to protect your personal property just get it insured as it is easy to replace but your life is not easy to replace. Using arms (deadly force) is only acceptable in self defense or defense of others if life or severe bodily injury is going to be used against you. FYI, rape is considered by most jurisdictions to be justifcation for the use of deadly force; even here in California!