Balanitis: This is an inflammation of the glans penis and is common in uncircumcised boys. It can be caused by poor hygiene, infection, or an allergic reaction. The swollen foreskin in a 5-year-old could be a result of balanitis, especially if there's a history of not retracting the foreskin for cleaning.

Phimosis: This condition involves a tight foreskin that cannot be fully retracted over the glans penis. It can lead to swelling and is common in young boys, though it may not always cause noticeable swelling unless there's an attempt to retract the foreskin.
Urinary Tract Infection (UTI): While less common in boys than in girls, UTIs can cause symptoms such as dysuria, frequency, and in some cases, swelling of the genital area, including the foreskin.
Contact Dermatitis: An allergic reaction or irritation from soaps, detergents, or other substances can cause the foreskin to become swollen and inflamed.

Paraphimosis: This is a medical emergency where the foreskin is retracted behind the glans and cannot be returned to its original position. It can cut off blood flow to the glans and requires immediate attention.
Testicular Torsion: Although it primarily affects the testicles, severe pain and swelling can sometimes be referred or associated with swelling in the genital area, including the foreskin, especially if the child is too young to accurately describe their symptoms.

Malignancy: Though extremely rare in children, certain types of cancer (like penile cancer) can present with swelling or lesions on the penis, including the foreskin.
Granuloma: A granuloma, which is a small area of inflammation, can form on the foreskin due to various causes, including infection or trauma, leading to swelling.