S., please don't discard something just because you haven't found enough information on it. There's plenty of information on alternative therapies for adults,children, pets, what-have you, you just need a little patience to find it. Colloidal Silver is great for fighting persistant infections, in fact, it is called by many a "hospital in a bottle". That being said, not all CS is the same. Many people try to make it at home without knowing exactly what they are doing and hence create a less than pure or useful product. It is the overuse of these kinds of products that will give bad results. Health food and online stores sell pure quality bottles of Colloidal Silver that you can take and give your child without turning him into a silver dollar :-)
Besides CS, there are many different natural approaches to boosting the immune system, but it is never wise to just rely on any one thing. A proper diet which restricts white flours, processed foods and sugar, plus adding plenty of fresh fruits and vegetables is a major start. You can give your child pediatric formulations of Echinacea and Golden Seal, along with lots of vitamin C. There are many other approaches that combined will strengthn and heal your child.
Here is a link to a huge alternatives website which will answer many of your questions (you can even ask one yourself and you'll get an answer)and you will also read about many other useful things that will be new to you.
http://curezone.com/forums/f.asp?f=97
http://curezone.com/
It is good that you are being very cautious about what you administer to you child, but in doing so, make sure you're not,.....ahem,..er, throwing out the baby with the bathwater. Your Mom means well, she is probably concerned about the amounts of antibiotics that her grandchild has been taking and for good reason. It is much better to strengthen the body naturally than to load it with medications after it has become sick.
Oh, and please don't pay too much attention to Quackwatch. There are high rewards for coming against alternatives, but besides that, they were taken to court not too long ago and they were found to be greater quacks than the people they try to smear. So just proceed with caution and read, read, read!