Althusser believed the family was a feature of the ideological state apparatus, along with education, religion and the mass media.
Society cannot function through force alone- ideology is key to maintaining social control.
Institutions have moved from the public to the private sphere, and under bourgeoisie control.
Institutions like family, education and religion make up the ideological state apparatus and are used to spread bourgeoisie ideology and keep the proletariat in false consciousness.
Institutions like police and the army are part of the repressive state apparatus and use force to achieve social control.