A good protocol to have in place with newly born animals is for both puppies and kittens to be wormed at 2 weeks of age, 5 weeks, just before they leave the breeder and then again at 8-12 weeks. We would further advise monthly worming until 6 months of age, then the frequency of worming becomes dependant upon the product you wish to use and the risk of exposure.
It is important to worm your pets for many reasons. They can cause diseases in people especially young children who may not be as thorough with hygiene. When young the worms can damage the lining of the gut and so the puppy or kitten can’t absorb the goodness from the food as they should.
Worms can be picked up anywhere as they are widespread. Puppies and kittens most frequently get infected by their mothers via the milk. Therefore we normally recommend worming every two weeks until your puppy or kitten is 12 weeks, then every month till they are 6 months and then 3 or 4 times a year.