This is a tip that applies to ciswomen only: being pregnant or nursing your entire post-puberty life greatly reduces your risk of breast cancer. At least if you are a female rat.
There is an INCREDIBLY HIGH rate of breast cancer in female pet rats. Why? Because evolution's programming is for them to be pregnant or nursing - or both at once - all the time. Pet owners, however, not wanting to find homes for all those ratlings, don't tend to let that happen. So they get breast cancer a lot.
For human women, it's a bit different. There is a slightly lower risk of having breast cancer if you have at least one child, especially one before you turn 30. There is an additional slightly lower risk if you have many children - the main theory is because you have fewer menstrual periods. I'm not sure about the details on how that helps, the scientists might not know yet.
Of course, having one (or more) child(ren) just to reduce your risk of cancer is not doing justice to the child(ren). Gods know, parenting is rarely about the parent, when done right.