Background: There is considerable evidence that health systems, in so far as they ensure access to healthcare, promote population health even independent of other determinants. Access to child health services remains integral to improving child health outcomes. Cognisant that improvements in child health have been unevenly distributed, it is imperative that health services and research focus on the disadvantaged groups. Children residing in urban slums are known to face a health disadvantage that is masked by the common view of an urban health advantage. Granted increasing urbanisation rates and proliferation of urban slums resulting from urban poverty, the health of under-five children in slums remains a public health imperative in Malawi. We explored determinants of healthcare-seeking from a biomedical health provider for childhood symptoms of fever, cough with fast breathing and diarrhoea in three urban slums of Lilongwe, Malawi. Methods: This was a population-based cross-sectional study involving 543 caregivers of under-five children. Data on childhood morbidity and healthcare seeking in three months period were collected using face-to-face interviews guided by a validated questionnaire. Data were entered in CS-Pro 5.0 and analysed in SPSS version 20 using descriptive statistics and logistic regression analyses. Results: 61% of caregivers sought healthcare albeit 53% of them sought healthcare late. Public health facilities constituted the most frequently used health providers. Healthcare was more likely to be sought: for younger than older under-five children (AOR = 0.54; 95% CI: 0.30-0.99); when illness was perceived to be severe (AOR = 2.40; 95% CI: 1.34-4.30); when the presenting symptom was fever (AOR = 1.77; 95% CI: 1.10-2.86). Home management of childhood illness was negatively associated with care-seeking (AOR = 0.54; 95% CI: 0.36-0.81) and timely care-seeking (AOR = 0.44; 95% CI: 0.2-0.74). Caregivers with good knowledge of child danger signs were less likely to seek care timely (AOR = 0.57; 95% CI: 0.33-0.99). Conclusions: Even in the context of geographical proximity to healthcare services, caregivers in urban slums may not seek healthcare or when they do so the majority may not undertake timely healthcare care seeking. Factors related to the child, the type of illness, and the caregiver are central to the healthcare decision making dynamics. Improving access to under-five child health services therefore requires considering multiple factors.