Everyone i know here just walks into each others homes, but im not comfortable with that, i have been taught to always knock and wait for someone to answer the door, my friends laugh at me but i think its good manners. Id say these boys are used to just walking in to someones home, but how scary they could have been anyone. And at my mums, she never locks her house up as she has inside dogs but one day someone walked into our house and ransacked my bedroom, i came home from school and my bedroom door was opened and my room was trashed, they had stolen only DP's laptop which was under my bed so they knew what they wanted.... i didnt sleep in there for weeks..

Good on your DS for saying to knock next time