Despite the rampant myths, taking care of an intact penis is not complicated at all. Most of the text that follows below are things to avoid doing and situations to watch out for, rather than things that need to be done.
Infancy / Early Childhood
"If intact, do not retract. Only clean what is seen." There is virtually no reason to retract a boy's foreskin -- not to "clean" it, not to "inspect" it, not to insert a catheter. To wash a child with a foreskin that is still fused to the glans, simply use clean warm water and wipe the outside much the same way you would their fingers. While the foreskin is still tightly fused, the flow of urine is usually able to push out any debris that happen to find their way into the foreskin opening. Soaps can irritate the inner foreskin and glans. Bubble baths might be problematic for that reason - just use clean water while he is just sitting and playing in the tub. If you wish to introduce bubbles, start out with a small amount of a very mild bubble bath solution and keep watch for signs of irritation during and after the bath. Once a boy "finds" his penis, he may do a lot of tugging on it, and sometimes it might seem like he will hurt himself. Relax. It is natural, and he isn't going to deliberately cause himself a painful injury, especially down there. It might, however, cause a bit of irritation, especially if the tugging initiates separation and retraction of the foreskin (see below).
Preventing forced retraction by the hands of others: As a parent, you can be very well-informed about not forcefully retracting your son's foreskin and never do such things yourself. However, your child's doctors, relatives, and day care providers might not be so knowledgeable. You need to have the resources to address this concern from the moment your son is born, because even the doctors and staff in hospital delivery rooms and nurseries can be misinformed about normal penile development. Visit our list of local "intact-friendly" doctors.
"Ballooning" is normal: On some boys, the opening of the foreskin might be slightly too narrow to allow urine to pass through as quickly as it is coming out of the urethra. In these boys, and even occasionally in all boys, this momentary buildup of urine pressure inside the foreskin will cause the foreskin to expand slightly, similar to a balloon being filled with air or water. If the foreskin is no longer adhesed to the glans, the full length of foreskin can expand and the apparent size difference may be startling for the uninitiated. This is normal, and is no cause for alarm, as long as there is a steady urine flow and all the urine empties as the flow slows. If the urine is being held back to the point where the pressure is painful, the urine stream seems abnormally narrow or inconsistent, or the urine isn't completely voided from the bladder-urethra-foreskin, consult an intact-friendly doctor. This could be a sign of an infection or tissue irritation at some point along the urinary tract.
Later Childhood / Natural Retraction
The age at which the foreskin will naturally separate and become retractable varies widely from individual to individual, but averages around age 10. As the foreskin separates from the glans, and the surfaces of the glans and inner foreskin become exposed to air and clothing, there might be a period of time where these new sensations are annoying, perhaps even to the point of being irritating. It is important that the boy knows this is a completely normal process, and the extreme sensitivity should eventually settle down.
If odors become an issue, it usually points to a problem with overall hygiene or possibly to a urinary tract infection, not a problem with the foreskin or penis itself. Most commonly, the odors are from either heavy sweating in the groin area, residual urine remaining in the foreskin, infrequent/ ineffective cleaning, or a combination thereof. These problems are usually solved by a simple change in clothing and/or the daily routine. For instance, change to a lighter weight, breathable underwear. With restroom visits, make a conscious effort to squeeze out all of all the urine from the urethra/penis (and perhaps dabbing the last few drops on a piece of toilet tissue). Bathe more often - especially as puberty starts. Once the foreskin becomes retractable, he should be pulling it back during baths or showers to rinse off any debris or urine inside. Soap is not generally needed on the glans or inner foreskin, and may actually irritate those parts of the body. If soap is wanted, it should be as mild of a soap as possible, which generally means a fragrance free moisturizing bar/lotion, not "real soap." By the time he is bathing himself, he should be aware of which soaps he can use and which will cause irritation.
Adolescence / Adulthood
Once puberty starts, perhaps even earlier, your son will want to have more privacy and less parental involvement with his body. His body is changing: the voice deepens, facial hair develops and body hair thickens, the composition and amount of skin oils and sweat changes, genitals enlarge, and semen starts being produced. New odors begin coming from nearly every part of the body. Even though he wants less direct involvement from you regarding his hygiene, it is still okay to give reminders (the occasional demand might be necessary) to keep his whole body clean - including properly washing his genitals. Continue reassuring him that his foreskin is a completely normal part of his body. Give him reassurance that you will be available for any questions he might have or situations he might notice. Setting the stage now for proper self-care is important for all aspects of his body, not just his foreskin, and will somewhat help ease the upcoming social situations such as dating and entering the work force.
An adult with good overall hygiene practices will rarely have any problems with his foreskin. That being said, cancer can be found in any and all parts of the body - including the testicles and penis. It is important to know the signs and symptoms of both, even though penile cancer is exceedingly rare, and have a good relationship with your primary care physician to answer any questions that might arise.
Additional resources
Peaceful Parenting: Basic Care of the Intact Child