The objective of this review was to evaluate attention and executive function performance in children with neurodevelopmental conditions across the first 5 years of life, compared to neurotypical peers. MEDLINE, EMBASE, and PsycINFO databases were searched until June 30, 2023, and studies comparing attention or executive function between children with (or at risk for) neurodevelopmental conditions and neurotypical (or low risk) peers, 0 to 5 years old, were included. Of the 4338 studies identified, 111 studies with 12292 participants were included in the meta-analysis. The qualitative analysis of brain development included 5 studies. Primary outcomes were the standardised mean difference (Hedges' g) in attention and executive function between groups. Meta-regressions examined moderating effects of age, biological sex, diagnosis, and measure type. Children with neurodevelopmental conditions showed small delays in attention (n = 49 studies, k = 251 outcomes, g = 0.36, 95% CI 0.23-0.48, p < 0.001) and moderate delays in executive function (n = 64 studies, k = 368 outcomes, g = 0.64,95% CI 0.53-0.76, p < 0.001). Attention and executive function delays could not be identified in the first year (equivalence tests, p < 0.001), small to moderate delays were found in toddlerhood and moderate delays by preschool. Delays identified were largely transdiagnostic, although there was some evidence of diagnosis-specific delays for attention and moderation by measure type (informant rating vs performance-based vs physiological). Qualitative analysis described how delays were underpinned by a divergence of brain development in medial prefrontal regions. These findings highlight the potential of using attention and executive measures to detect delay and to intervene in neurodevelopmental conditions early in life.