
If they were taking milk from mum after being wormed at 3 weeks of age, the larvae pass through the milk to the puppies that is why you saw worms after worming them on Saturday.
We worm our pups every fortnight until they are 12 weeks of age, then monthly up until 6 months of age. After that we routinely worm every 3 months whether we see worms or not.
If you continue to see worms then ask for a worm count at the vet, drontal puppy only worms for roundworms, it is possible but not very likely that they may have picked up other species, in which case you need to ask your vet.