There are 11 million children - under-18s - in England. During 2016, over 390,000 children received some form of support from social care services; over 58,000 children were judged at risk of abuse
During a 2015-16 survey period, around 2.7 million adults took illicit or controlled drugs; 2.5 million adults reported regularly drinking over 14 units of alcohol per day.
There’s an overlap. Its size is difficult to identify, since none of the published studies account for overlaps and most don’t have compatible sample sizes or time periods. Nonetheless, in 2012 a Full Fact review suggested between 950,000 to 1.9 million children are living with parents who are addicted to drugs or alcohol.