The objective of this study was to test whether adding a text message campaign about the importance of eating eggs and other nutrition-related behaviours to an on-going package of large-scale, diverse social and behaviour change interventions would improve four types of nutrition-related knowledge and behaviour outcomes: child diets (egg consumption as the primary outcome), maternal diets, maternal nutrition knowledge, and maternal participation in additional interventions. The cluster-randomized controlled trial involved a repeat cross-sectional design, recruiting families with children 12-23 months of age at baseline and endline in one plains district of Nepal. Throughout the 1000-day period, 51 text messages were sent to each household at specific time points to reinforce ideal diets and other nutrition-related practices and promote engagement with community health workers and other intervention platforms. The primary outcome was egg consumption and dietary diversity among young children. We found no population-level effect. Some evidence supports that for those who received and opened the SMS intervention, it improved child egg consumption (odds ratio [OR]: 1.41, 95% confidence interval [CI]: 1.03-1.93), child minimum dietary diversity (OR: 1.36, 95% CI: 1.07-1.73), child dietary diversity scores (β: 0.15, 95% CI: 0.01-0.24), as well as maternal IYCF knowledge (β: 0.21, 95% CI: 0.08-0.35), participation in health mothers' groupmeetings (OR: 3.03, 95% CI: 1.91-4.84) and Bhanchhin Aama listenership (OR: 1.36, 95% CI: 1.07-1.73). This study highlights the importance of more research to understand the effectiveness of emerging digital interventions for behaviour change among specific populations, to facilitate nuanced targeting to those who can best benefit from these investments. Registered at clinicaltrials.gov with identifier NCT03926689.