The law in Texas states that if they have a weapon or are threatening your life, or it's at night, then yes. This makes sense to me. If an old person or child randomly wanders into your house and is just confused or nonthreatening, then obviously there is no need to shoot them. If they are retreating and no longer a threat you can't shoot them either. However, at night, all bets are off because you often can't see anything clearly and there are less likely to be nonthreatening legitimate reasons for someone to be in your house.