Shock Absorbing Front Forks
 

I was just wondering what kind of maintenance, if any, these require. I recently purchased 3 bikes for the family, a Raleigh Mojave 4.0, Cannondale Mountain Bike, and 2000 Giant Cypress DX Ladies bike, and all of them have shocks up front. I'm pretty sure nothing has ever been done to them, and I'm not sure what I'm getting into to. They all seem to work fine. Is it better to leave well enough alone?

The Rock Shox on my MTB is over 20 years old, has never had a thing done to it, works fine. I guess I top up the air every couple of years. A suspension fork, mounted on a bike used mostly on the street or mild dirt trails, is doing very little - occasionally compressing an inch or so, but most of the time nearly rigid. No reason to do anything to them until they give you trouble. They probably never will.

Now that's the kind of advice I like! Do nothing! I wondered how important it was, because I doubt these bikes ever saw any trail time what so ever. Thanks!

After a muddy ride wipe off the upper stanchions - fine bits of mud (particularly clay) wiggle past the seals and slowly build up in the lowers.

Not necessary with "upside down" forks, although these are rare.

Depends on what type of shocks they are, and how heavily used they are. Basically shocks come in three flavours: elastomers(=rubber cushions), oil/spring and oil/air.
Elastomers may wear out, even fracture due to use and age. But if you're staying(almost) exclusively on roads, a collapsed fork may not be an entirely bad thing.
Oil/spring are very robust. They "should" have the oil replaced at some sort of interval, and may eventually wear the seals down to the point of poor shock absorption. But for casual riding with little contamination their lifelength is indefinite, and the advantage of preventative maintenance fairly marginal. Prices being as they are over here, I reckon 4-5 services would equal the price of a new fork if you stick to the inexpensive models.
Oil/air are the most delicate of the lot, with recommended service intervals as low as 30 hours for some models. But that's mainly driven by exposure to contamination, and the amount of compression they regularly see.
For casual riding, check the sag/air pressure every now and then and you're OK.