Background: Diabetes presenting in children or young adults and terminating in fatal ketoacidosis first appeared in the medical literature in the 19th century, but this was a very rare clinical condition. The aim of this study was to determine the effect of Type 1 diabetes mellitus on children and the role of mother’s knowledge on the effect of the type 1 diabetes mellitus on children. The sample was taken from successive admissions to the outpatient diabetes clinics and impatients at Maternity & Children Hospital at Makkah which is a tertiary care. Methodology: A cross-sectional design was adopted in the present study. Results The participants were found to be between 20 to 30 years old, the majority of the participants were female comparing to male with a statistically significance of (T=-3.818, p<0.001); the majority of the participants were found to have intermediate education with a statistically significance of (F=8.540, p<0.001); the majority of the participants were had an occupation with a statistically significance of (F =4.513, p<0.001) Recommendations: The information presented in this study should be reinforced in order to promote sustained behavioural change in the community; therefore, there is a need to increase research studies on T1DM in Saudi Arabia.