This puppy just get separated from it's mother at day 40th and then they met each other after one month. Puppy just remembered her mother and showered her love towards its mother.
You can't deworm them now. But you said puppies are not eating well so take your puppy to vet for checkup. And check whether the mother dog providing sufficient amount of milk to puppy. Sometimes mother dog can't able to provide sufficient amount of milk due to deficiency.
