In Real Life, theoretically it should be possible for two women to have a biological daughter by a process called haploidization, or through creating sperm cells from one of the two mother's bone marrow. (But women alone couldn't produce a son, due to the lack of a Y chromosome.) For males, there is research being conducted on the creation of male eggs, which consists of removing the nucleus of an ovum and replacing it with the nucleus of a sperm. This new egg would then be fertilized by sperm from the other father. The process has been documented in mice and its viability in human reproduction is still being developed. It is also theoretically possible to achieve male pregnancy by implanting an embryo in the abdominal cavity, but risk factors make it unlikely that this will be tested.
Alternatively, a same-sex couple where one half is transgender can bear a biological child if the trans partner's genitalia hasn't been altered. While hormone therapy will halt sperm production or ovulation, a trans person who wishes to conceive can temporarily go off the hormones if they so desire.