We provide an account of the developmental trajectory of Emirati Arabic negation particles. We treat the non-verbal predicate negator (NVPN) "mub" as a negative copula, in contrast to the verbal predicate negator (VPN) "maa," which encodes sentential negation in verbal and existential contexts. The analysis is supported by evidence from a longitudinal corpus of six Emirati children. Given the high frequency of occurrence of "maa" in the ambient language, we show that an input-frequency account predicts "maa-mub" substitutions in early stages of acquisition. However, confirming previous findings by Becker we show that when "mub" emerges in later stages, its distribution exhibits an asymmetry: "mub" is used frequently with individual-level nominal/adjectival predicates but it almost never appears with stage level adjectival/prepositional/ adverbial predicates, mirroring the distribution of copular elements in child English (and other languages).