The "yes" campaign has dedicated its first salvo in the same-sex marriage debate, arguing the only people who will be affected by changing the Marriage Act, are those who are gay.

But conservative senator Matt Canavan said he remains concerned same-sex marriage was only the "first step" in a wider change of society's values, and argued relationships between males and females deserved "a special word and a special institution" for their ability to produce children.

The Coalition for Marriage released its first television advertisement on Tuesday opposing any change to the definition of marriage, by claiming a "yes" vote would lead to children being forced to learn radical gender and sex theories.

In its first advertisement, released on Wednesday, Australian Marriage Equality directly tackled its opponent's campaign, with Dr Kerryn Phelps telling viewers that "sadly, some are trying to mislead us … by saying it will have a negative impact including on young people".