Objective To investigate the effects of sanitary toilet improvements for early childhood on long-term health outcomes among rural children in China, thus providing empirical evidence for informing future health policies targeting children in rural areas.

Methods This study utilized longitudinal data from the China Health and Nutrition Survey (CHNS) spanning the period from 1991 to 2015, examining 2 929 rural children aged 7–18 years with documented information on their sanitary toilet improvements during early childhood (ages 3–6). A two-level mixed-effects model was employed to assess the health effects of sanitary toilet improvements. Additionally, a multilevel mediation analysis was conducted to examine whether improvements in household sanitary environment mediated the relationship between sanitary toilet improvements and children′s long-term health outcomes.

Results The height-for-age Z-scores (HAZ) for the 2 929 rural children aged 7–18 years ranged from –5.73 to 5.02, with a mean of –0.61 ± 1.25. Among these children, 982 (33.5%) received sanitary toilet improvements during ages 3–6, while 1 063 children (36.3%) experienced fecal contamination exposure in their household sanitary environment. Multilevel regression analyses revealed that receiving sanitary toilet improvements during early childhood (ages 3–6) enhanced long-term health outcomes (β = 0.22, 95%CI: 0.06–0.37, P = 0.006). The health benefits were more pronounced among children from families with lower per capita household income than among their higher-income counterparts (β = 0.34, 95%CI: 0.01–0.67, P = 0.041). Children from nuclear families experienced smaller health gains from sanitary toilet improvements than those from non-nuclear families (β = –0.38, 95%CI: –0.70 to –0.07, P = 0.018). Within the same household, the health-promoting effects of sanitary toilet improvements diminished as children grew older (β = –0.25, 95%CI: –0.42 to –0.08, P = 0.004). Mediation analyses demonstrated that sanitary toilet improvements indirectly affected child health through improved household sanitary environment (β = –0.071, P = 0.019), with better household sanitary environment promoting health development (β = –0.174, P < 0.001). Age functioned as a negative moderator in the pathway linking household sanitary environment improvements to child health (β = 0.126, P = 0.013). Spillover effect analyses indicated that sanitary toilet improvements by other households in the village generated positive spillover effects on children′s health (β = 0.257, P = 0.001).

Conclusions Sanitary toilet improvements for early childhood in rural areas of China promote long-term health outcomes among children, with health benefits mediated through improvements in household sanitary environment.