A pup won't get heartworm until after 6 months of age. I use a good quality fly spray on the mother, apply it to her back away from the pups and allow her to dry. Also spray the dog house inside and out and allow to dry as well. You could also put yard spray on the ground surrounding the kennel and allow to dry before placing them out there. And I always keep my grass cut short to minimize mosquitoes and ticks.

S_B