How long before a cast can be put on a 3 yr old's broken elbow?

Splint while swollen: The longer term cast is generally delayed until the initial swelling of the injury has subsided. This allows a snug fit so the cast will not allow excessive movement while the bones mend. Swelling tends to peak at 3 days+/- & subside enough after 5d- a week to cast. Timing can vary & the clinical judgment of the physician can decide if it's too early or late to cast.