Christy Lee is exactly right about how to remove a tick. You never want to yank it out or cover it with oil, Vaseline etc..
I want to add: KEEP the tick! Place it immediately into a ziplock plastic bag. Don't smash it. Take it, and your son, to the doctor right away and tell the doctor to send the tick for testing. (If it's too late for this time and you alredy got rid of the ticks from yesterday I'd still let the doctor know your son was bitten.)
Labs can test ticks for Lyme and other diseases. If you keep the tick and get it tested promptly, the doctor can start medication for a bitten child much sooner than simply waiting to see if a rash or symptoms appear! Sick tick means start meds. Waiting for symptoms in a child means a delay in getting that treatment started.
Also, DEET is truly the best preventative as others note. And long pants are frankly a must -- ticks love warm, moist, dark spots and that means groins and armpits as well as in the hair, and shorts are a recipe for ticks to reach the groin area. A friend kept finding ticks on both her sons' groins all summer since her ex had a farm and didn't "believe" in protecting the boys from ticks there or inspecting them before he sent them home to mom. So always inspect the whole body including groin and genitals.
There is a substance called permethrin that you can buy at outfitter shops (REI, Hudson Trail Outfitters etc.) It repels ticks etc. from clothing and sleepng bags and tents. It's only for use on fabrics, not on humans, but once it's on the fabric and dried, your son would have to pretty much try to mouth the fabric or bury his face in it and rub in order to pick it up. You might have a pair of "hike pants" for him that are lightweight long pants sprayed with permethrin, as well as hike socks that are also sprayed and cover his ankles up to about halfway up the shin.
Hats, vital. You can spray hats with permethrin or just with your DEET-based skin spray but the latter would have to be done each time.
I have not heard the 48-hour rule. Ask your pediatrician. But be aware that the famed "bullseye shaped rash" that is typical of Lyme disease does not always appear! My friend's child got Lyme and they never saw any rash at all, and never even knew she'd been bitten. The doctor told them that the rash is not always there. If your son has cold- or flu-like symptoms, fatigue, etc. that he can't shake, even a few months from now, that can be Lyme --that's how this family (and a very sharp grandma who realized the cold-like symptoms could instead be Lyme) found out this girl had it. She was put on a long course of antibiotics and has been perfectly fine for years, because her family was alert.