I am not sure of this question very well.
However, keeping gap between two child (human beings I suppose) is part of family planning. There are contraception and fertility control methods available and known to many nowadays.
Sterilization process - surgical
In males - vasectomy
in women - tubal ligation
For women there are many methods,
harmonal contraceptives - birth control pills, emergency (contraceptive) control pills,
implantable contraceptives or rings
male or female condoms
By mating/having intercourse during the times when fertilization of eggs is least probable.