Esp if the adult cat(s) are females, they may just be cleaning up after the kitten like they would do for their own.
Strongid is for roundworms. You might take a fresh (not more than 2 hrs old) stool sample to your vet to have them do a microscopic test for other parasites.
You should be feeding kitten food. Use the same kind all the time if you find one that agrees with her digestive system. You don't need to keep changing kinds because you think she's bored. Read the food labels: most of the cheaper foods are composed mainly of grains, animal by-products, and other garbage. This is not a chicken, it's a cat. Try to feed foods that have meat as the first two ingredients. Many cats (& dogs) are allergic to corn or wheat, brewer's yeast, etc. ("By-products" have no real food value, they are waste: beaks, combs, feet, various cheap guts, cancerous lumps, etc. And you don't even want to know what "digest" is!)
If this new kitten wasn't exposed to a litter box (or a place to dig) when it was younger, it may not realize what the box is for. Although it seems instinctive in most kittens & cats, there are some that seem a little "slow" to understand.
If this kit were mine, I would use a largish (perhaps dog sized) crate, preferably the wire kind instead of the plastic kind, if available. Fix the crate up with litter box, bed and dishes. If the crate seems too large, put an empty closed box or something in there to take up the extra space. It's best if she has the choice of relieving herself either in her bed or her litter box, and nowhere else. Most cats won't use their bed, so hopefully that would encourage her to use the litter box.
This isn't a prison. She can have safe toys. If you want to play with her, take her out and play with her, or hold her in your lap while you're watching TV. But if you aren't paying DIRECT attention to her, put her back in the crate. NO UNSUPERVISED HOUSE ROAMING! If you've got kids who can't follow rules, padlock the kitten into the crate.
If she pees/poops in the litter box, don't race to clean it out. Leave it there so she knows that's an okay place. If she doesn't cover it, you can cover it with the litter to cut down odor. Try to leave one poop or pee in the box as a reminder.
Some basic rules:
* Put the crate out of the way, but keep it where the family is, not down in the basement or out in the laundry room. Don't put it where it could be kicked or where loud noises happen (washer or dryer, etc).
* Use only plain cat litter, clumping or non-clumping; no perfumes, no additives, no unusual materials (pellets).
* No Litter Maid or other automatic litter box.
* No violence toward the kit if someone in the family takes her out and leaves her out and she pees or poops, unless you want to beat the human that did it.
* This training can take 2 to 4 weeks. Be patient. The problem probably didn't start overnight, and it's not going to end overnight, either.
* Once she starts using the litterbox regularly, don't be too quick to end the training. Let it become a habit.
* Use a good odor neutralizer where she has peed/pooped in the past, and be sure to use ENOUGH, about 1.5 times as much solution as there was urine, for example. Follow the directions.
Once she's using a box and you let her out of the crate, try to pay attention to what she's doing. Accidents? Return her to the crate.
Never put any litter boxes in high-traffic areas, esp where they might be kicked. Most cats prefer privacy and quiet. Multiple cats? Have multiple litter boxes, and keep them scooped.