The primary objective of this study is to evaluate the efficacy (as measured by induction of remission) of two dose levels (low and high) per age group (5 to <12 and 12 to ≤17 years) of budesonide rectal foam as compared to an equivalent volume of rectally administered placebo foam over the same dosing schedule, in pediatric subjects with active, mild to moderate distal ulcerative colitis (UC).

Inclusion Criteria:

1. Male and Female (non-pregnant and non-lactating) 5 to ≤17 years of age at Screening.
2. Established diagnosis of UC, based on clinical history, characteristic endoscopic findings, and histopathology results from biopsies.
3. Disease limited to the distal colon and rectum, (disease involving only the first 15 centimeters or less proximal to the anal verge).
4. Active, distal UC of mild or moderate severity, defined as a Modified Mayo Clinic Score (mMCS) between 4 and 8, inclusive, that includes an endoscopy subscore ≥ 2 and a rectal bleeding subscore ≥ 1.
5. If on a background oral 5-ASA, the dose and formulation have remained unchanged for at least 6 weeks prior to Visit 2 (Run-In) and the subject is willing to remain on the same dosage form and regimen for the duration of the study.

Exclusion Criteria:

1. Current or prior diagnosis of Crohn's disease or indeterminate colitis.

2. Ulcerative colitis involving the proximal colon - i.e, the sigmoid, left, transverse, and/or ascending colon and cecum;

3. Severe UC, defined as an mMCS > 8.

4. Infectious colitis (based on positive microbiologic tests at Screening) or any recent history of infectious colitis (within 30 days of Screening).

5. Prior gastrointestinal surgery, except appendectomy or hernia (e.g., inguinal, umbilical).

   NOTE: Prior cholecystectomy is not exclusionary if more than 1 year prior to Screening.

6. Evidence or history of toxic megacolon or bowel resection.

7. Active proctologic pathology such as hemorrhoids, fistulas and fissures or other historical anatomic problems which would impair rectal administration (e.g., cloaca, imperforate anus history)