How do we as muslim parents bring the topic up? My son is young, but like someone mentioned time flies and sooner than later he'll start to grow older in this culture. How do you teach them the proper way, and hope they will abstain?
It's a very good question and the answer can be very tricky and is sensitive depending on the situation when you are talking to the child.
First of all, just to clarify and I am sure you know this, your husband should talk to your son about this topic. If you have a daughter, you should talk to her. That way both the child and the parent will feel comfortable and would ask any questions that he/she may have.
As for HOW to address, I am not a parent yet, so I am sure others will have practical answers, but if I were the parents and it was time for me to talk to my son, this is what I would do:
Instead of taking the child into a room and talk about it in a serious environment, I would take him out on a "father-son" day and we would probably go out and eat.** Also*, I would tell him in advance what this trip will be about so that he is mentally prepared to talk about it or ask any question. Then I would shed some light on the topic both from religious perspective **AND* worldly perspective (i.e. STDs, responsibilities etc.).
I would also give him a chance to communicate back and ask any questions. Most desi parents (at least my dad) don't give a chance to children to ask any questions. They would "lecture" and tell what's on their mind and then that would be the end of it. I am sure there are exceptions but this is what most of my friends' parents do as well. So please avoid this. Any discussion should be two-way, otherwise it's rather a message.
EDIT: Niksik you guys have a great plan and that is how I plan to raise my kids. There's a fine line between being friendly with kids and being too nosy and it seems like you guys are aware of that line. Unfortunately by the time most desi parents want to become friends with their kids (in teens or later), by that it's too late. Kids are kids, at times they will even "hate" their parents but that's them. The key is to respect the fact that they need their space and they can't be all friendly and all sharing at all times. Again, sounds like you already know all this and you have a very good plan that will work out very well when executed. Good luck :)