FPA, formerly the Family Planning Association, said the comic would be available for all UK schools to buy.
The 12-page booklet asks children to identify what the differences are between the two genders.
Parents have the right to prevent their children from seeing it but family campaigners have called it an attack on children's "natural modesty".
The pamphlet is called Let's Grow with Nisha and Joe and the FPA hopes it will encourage discussion about the facts of life at a young age.
Topics covered include naming parts of the body, the importance of family and friends and how to keep safe.
The charity's chief executive, Julie Bentley, said: "Sex and relationships education at this age is about learning basic information and skills, in exactly the same way that children start with ABC when they begin to read and write.
She said the six and seven-year-old target age group wanted to talk about their feelings, bodies, and relationships.
"It's important that they have this information before their bodies start to change.
"Talking about body parts is often easier for children when they are younger as they are less self-conscious and less sensitive about their bodies."
But Norman Wells, director of Family and Youth Concern, said it was up to parents and carers to teach sex education to children.
"This is all part of an exercise to break down children's inhibitions and natural sense of modesty.
"Most parents would be very concerned if they knew that their children were being given literature at school produced by an organisation that doesn't put sexual intimacy in a clear moral context and that fails to respect the role of parents."
