Your child may keep getting worms, especially pinworms (also called threadworms), because these are highly contagious parasites common in children aged 4 to 11. The worms lay eggs around the anus, which cause itching. When children scratch the area, the eggs get under their fingernails and can be ingested again if they put their hands in their mouth, causing reinfection. The eggs can also spread indirectly through contaminated surfaces, food, dust, or toys. The eggs can survive outside the body for up to two to three weeks, making transmission easy even with good hygiene.

Children are more susceptible because they often have habits like thumb sucking, biting nails, touching contaminated objects, poor hand hygiene, and close contact with other children where worms spread easily. Pets are usually not a source of pinworms but other intestinal worms can come from unsanitary environments, contaminated water, or uncooked food.

Repeated infections are common because of the eggs' resilience and easy transmission. Treatments are available, but good hygiene measures and cleaning are vital to prevent reinfection. These include washing hands thoroughly, cleaning bedding and toys, and encouraging your child not to scratch or put their hands in their mouth. If symptoms persist, consulting a doctor for diagnosis and possibly stronger treatment is recommended.

In summary, your child keeps getting worms mainly due to the ease of pinworm egg transmission via scratching and hand-to-mouth habits, along with environmental persistence of the eggs and behaviors that facilitate reinfection.