AbstractBackgroundSurvival from pediatric critical illness in high‐income countries is high, and the focus now must be on optimizing the recovery of survivors. Muscle mass wasting during critical illness is problematic, so identifying factors that may reduce this is important. Therefore, the aim of this study was to examine the relationship between quadricep muscle mass wasting (assessed by ultrasound), with protein and energy intake during and after pediatric critical illness.MethodsA prospective cohort study in a mixed cardiac and general pediatric intensive care unit in England, United Kingdom. Serial ultrasound measurements were undertaken at day 1, 3, 5, 7, and 10.ResultsThirty‐four children (median age 6.65 [0.47–57.5] months) were included, and all showed a reduction in quadricep muscle thickness during critical care admission, with a mean muscle wasting of 7.75%. The 11 children followed‐up had all recovered their baseline muscle thickness by 3 months after intensive care discharge. This muscle mass wasting was not related to protein (P = 0.53, ρ = 0.019) (95% CI: −0.011 to 0.049) or energy intake (P = 0.138, ρ = 0.375 95% CI: −0.144 to 0.732) by 72 h after admission, nor with severity of illness, highest C‐reactive protein, or exposure to intravenous steroids. Children exposed to neuromuscular blocking drugs exhibited 7.2% (95% CI: −0.13% to 14.54%) worse muscle mass wasting, but this was not statistically significant (P = 0.063).ConclusionOur study did not find any association between protein or energy intake at 72 h and quadricep muscle mass wasting.