Functional Constipation: This is the most common cause of abdominal distention and constipation in children. It is often related to dietary factors, fluid intake, and bowel habits. The age of the child and the symptoms presented align well with this diagnosis.

Gastroenteritis: Although it typically presents with diarrhea, some cases can lead to constipation, especially if the child is dehydrated or has a prolonged course of the illness. Gastric air distention can occur due to swallowing air or as a result of the infection itself.
Lactose Intolerance: This condition can cause bloating, gas, and constipation in children who consume lactose-containing products but do not have sufficient lactase enzyme to digest lactose.
Food Allergy or Intolerance: Certain food allergies or intolerances, such as a cow's milk protein allergy, can lead to gastrointestinal symptoms including constipation and abdominal distention.

Intussusception: A serious condition where a part of the intestine slides into an adjacent part, potentially leading to bowel obstruction. It's a medical emergency that can present with abdominal distention, constipation (or obstruction), and sometimes currant jelly stool. Although less common, it's critical to consider due to its severe consequences if missed.
Hirschsprung's Disease: A congenital condition characterized by the absence of ganglion cells in the distal bowel, leading to functional obstruction. It typically presents in infancy but can be diagnosed later in childhood, especially if the segment of aganglionosis is shorter. Symptoms include constipation, abdominal distention, and failure to thrive.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can present with a wide range of gastrointestinal symptoms, including constipation and abdominal distention, although diarrhea is more common.

Cystic Fibrosis: While primarily known for its respiratory manifestations, cystic fibrosis can also cause gastrointestinal symptoms due to pancreatic insufficiency, including constipation and abdominal distention.
Neurological Disorders: Certain neurological conditions, such as spinal cord injuries or cerebral palsy, can affect bowel motility, leading to constipation and potentially abdominal distention.
Chronic Idiopathic Pseudo-obstruction: A rare condition characterized by impaired gastrointestinal motility without any mechanical obstruction, leading to symptoms like constipation, abdominal distention, and vomiting.