<b>ABSTRACT</b><br> <b>Background</b><br> Under the Children Act 1989 and other legislation, children’s social care (CSC) services in England have duties to promote and safeguard the welfare of children in their area, in particular children in need (CiN). It has been previously estimated that 14% of all children are CiN before age 5 and 23% are referred over the same period but is not known what proportion of children are ever CiN or referred to CSC across childhood. We used the CiN census (administrative records on all children referred to CSC in England) to estimate the proportion of children ever CiN or ever referred to CSC from birth to age 16. <b>Methods</b><br> The first full calendar year which the CiN census covers was 2009; our extract, which had complete data on school-aged children only, ran to 2014. We estimated the cumulative incidence of being CiN across three distinct cohorts: (1) those born in 2009 and age 4 in 2013; (2) those aged 5 in 2009 and 10 in 2014; (3) and those aged 11 in 2009 and 15 in 2013. For cohort 2, we used the estimates of Bilson and Martin (2016). For cohorts 2 and 3, we used Office for National Statistics mid-year population estimates as the denominator and the number of observed events in the CiN census as the numerator. We made allowances for the fact that there were events in our data that were of children with events in previous, unobserved periods (birth to age 4 for cohort 2 and birth to age 10 for cohort 3). Age-specific incidence estimates were combined to estimate the total cumulative incidence from birth to age 15 (i.e. before the 16th birthday). <b>Results</b><br> We estimated that 25% of all children are CiN at least once at any point between birth and their 16th birthday and that 43% are referred to CSC over the same time period. <b>Discussion</b><br> The estimates we have modelled, which must be considered preliminary, are large but plausible, especially for CiN. If correct, they have far ranging consequences for children’s services. The next step of this work will be to re-estimate the cumulative incidences using data on children of all ages with longer follow-up.