The four (arguably five) systems of the Model of Human Development, as Bronfenbrenner refers to his Bioecological Theory, are the micro, meso, exo and macro systems - supported by the chronosystem. Many factors influence a child's development and by splitting the effects into different "systems" it is easier to understand the effect and , in need take remedial steps to reduce unfavorable influences.
Please refer to the attached links and then to questions posed previously where the systems are outlined and explained, together with examples. This should help you to understand how each of these systems affects a child's development when they act individually and when two or more systems act simultaneously, which of course is often.
There are many contexts in which children develop - home, school, community and so on and these span out to include a wider scope encompassing cultural and historical patterns that may affect human behavior.
The complex nature of human development remains and a child who has a less than ideal family life may be more influenced by external factors - maybe those in the school system where a good role model - a teacher- can hopefully negate the negativitiy from one or more micro systems by its impact within the mesosystem.