As you may know, fluoride is used in dentistry to prevent dental decay. It can be taken up into the crystalline structure of enamel, replacing the normal hydroxyapatite crystal structure into a structure called fluorapatite. This can resist acid attack to a greater degree and there is a reduction of the solubility of enamel in acid. Prevention is far better than cure!
What's more, fluoride also has an inhibitory effect on oral bacteria which cause decay as they produce weaker acids and polysaccharides which diminishes the overall acid attack.
In most adult toothpaste, there is 1000-1500ppm F. As a general rule, there is NO need to use a lower PPM F toothpaste for children just use a small amount (pea sized). Encourage your child to spit out the excess paste and not swallow.
If you live in a water fluoridated area, there is an argument to use toothpaste at 500ppm F due to the lower risk factor.
High fluoride toothpaste should NOT be used fort children due to the risk of fluorosis. This is where adult teeth can develop with a mottled,chalky and discoloured appearance which is unaesthetic and very difficult to treat.
Mouthwashes generally have a lower fluoride concentration and hence are safe to use as an adjunct on a daily basis for children over six years old as long as they can spit out and not swallow. Non alcohol mouthwashes which are less harsh on the oral mucosa should be used.
Fluoride varnish such as Duraphat by Colgate can be a very useful treatment for those at high risk of tooth decay. The concentration is high, about 22mg/ml, and can only be placed by a dentist or therapist. It has been reported that such varnish applications can reduce decay rates by up to 46% in the adult dentition.
The question of toxicity always arises when fluoride is discussed. Thus far, there have no reported cases of acute toxicity due to ingesting toothpaste which is reassuring, However, as with everything in life, care should be exercised when young children are involved. Keep all oral care products out of reach and in a safe bathroom cupboard for example. If you suspect that your child has consumed excess fluoride, get them to drink lots of milk and seek immediate medical care.