Pain is common in children presenting to the emergency department but is frequently undertreated, leading to both short- and long-term consequences. Morphine is the standard treatment for children with moderate to severe acute pain, but its use is associated with serious side effects and caregiver and clinician concerns related to opioid administration. The investigators aim to determine if sub-dissociative ketamine is non-inferior to morphine for treating acute pain and a preferable alternative for treating acute pain in children because of its more favorable side effect profile and potential long-term benefits related to pain-related function, analgesic use/misuse, and mental and behavioral health outcomes.

Aim 1: To determine if IV sub-dissociative ketamine is non-inferior to IV morphine for decreasing pain intensity in children presenting to an ED with acute pain. The investigators hypothesize that IV sub-dissociative ketamine is non-inferior to IV morphine for decreasing pain intensity in children with acute abdominal pain or an extremity fracture.

Aim 2: To compare the rate of acute (<2 hours) adverse events, including cardiopulmonary adverse events, associated with IV sub-dissociative ketamine and IV morphine. The investigators hypothesize that there is a smaller proportion of cardiopulmonary adverse events associated with IV sub-dissociative ketamine compared to IV morphine.

Aim 3: To determine the relationship between ketamine and long-term sequelae of acute pain. The investigators hypothesize that children who receive ketamine will have better levels of pain-related function during the first week following ED presentation and will have greater odds of experiencing more favorable post-traumatic stress, anxiety and depression outcomes 1-6 months after ED presentation compared to children who received IV morphine.

Inclusion Criteria:

1. Abdominal pain or isolated long-bone extremity fracture (suspected or proven)
2. Self-reported pain score of ≥ 6/10
3. Requires IV morphine for analgesia as determined by the treating physician

Exclusion Criteria:

1. Weight > 82.4 kg
2. Known allergy/contraindication to morphine or ketamine
3. Antecedent receipt of ketamine related to presenting complaint
4. Inability to use self-report measures of pain or questionnaires
5. Chronic disease associated with pain
6. Chronic pain condition requiring use of opioids as outpatient
7. Hemodynamic instability or critical illness per treating physician
8. Altered mental state (e.g., GCS , 14 or clinical intoxication)
9. Known history of schizophrenia, liver or kidney problems, or osteogenesis imperfecta
10. Concern for open fracture, neurovascular compromise, or compartment syndrome
11. Injuries in addition to the extremity injury (e.g., head, neck, abdomen)
12. Known or reported pregnancy
13. Does not speak English or Spanish
14. Patient previously enrolled in this study
15. Wards of state, foster children, or children in custody

Consistent with the HEAL Public Access and Data Sharing Policy, one of our goals is to assure rapid data sharing. The de-identified Underlying Primary Data will only be shared when confirmed to be de-identified by the EMSC Data Center (EDC), according to the standards set forth in the Department of Health and Human Services Regulations for the Protection of Human Subjects, to ensure that the identities of research participants cannot be readily ascertained from the data. Underlying Primary Data will also be stripped of identifiers according to the HIPAA Privacy Rule. The EDC is familiar with these processes given their vast experience with data management. The de-identified data will be made available at the conclusion of the project period, and any manuscripts published before the end of the project period will have accompanying release of relevant deidentified data at the time of the manuscript publications.

The de-identified data will be made available at the conclusion of the project period (currently August 2029, but may be subject to an extension), and any manuscripts published before the end of the project period will have accompanying release of relevant deidentified data at the time of the manuscript publications. The investigators recognize that the NIH may require a particular repository to be used, but otherwise, the investigators intend to submit the end-of-study data to NICHD DASH, in which case the end date of access would be subject to NICHD DASH policies.

Because it is a condition of the NIH for newly funded studies to make data publicly available, the investigators are not sure what the future use may be. For our intended repository (NICHD DASH), applicants to receive the releasable data are required to abide by the User Agreement. The investigators note that if there are published manuscripts before the project period ends, minimal de-identified data would be made available to support the manuscript's reproducibility and enable further work. Such pre-trial-completion releases of deidentified data are to comply with Helping to End Addiction Long-term (HEAL) policies on data availability. The end-of-study deidentified data will be findable and available through the NICHD DASH repository's search functionality. The investigators will also note where the data are available in the primary study manuscript; as required for HEAL Initiative®-funded trials, the publications from this trial will be available as open access.