Martin Crew, director of Barnardo's Scotland, said good parenting was not linked to sexual orientation or whether a couple are married but to providing "emotional security and being a good role model".
He spoke out after becoming "increasingly concerned" at some of the arguments about family life being used in the debate over whether to legalise gay weddings.
Mr Crew said: "I do not believe that gay parents, or unmarried straight parents, will become better parents if they were to marry."
The Scottish Government launched its public consultation, stating it "tends towards the view" that same-sex marriage should be introduced, but that faith groups should not be obliged to solemnise the ceremonies.
About 50,000 of 70,000 responses to a Scottish Government consultation proposing gay marriage are understood to be against the proposal, although a recent survey found 69 out of 129 MSPs were in favour.
Research conducted by Ipsos Mori on behalf of the Equality Network, LGBT Youth Scotland and the Scottish Youth Parliament found 64% of people supported same-sex marriage, although 26% opposed same-sex marriage in places of worship.
However, the Catholic Church, the Church of Scotland, the Council of Glasgow Imams and the Episcopalian Church have registered objections to the legislation, arguing that marriage should be only between a man and a woman. The Humanists, the Unitarians, the United Reformed Church and the Quakers are among the groups who have no objection.
Mr Crew said he supports an equal right to marriage because it removed "yet another unhelpful distinction" between straight, lesbian, gay, bisexual and transgender families.
However, he said that as part of the debate, opponents of gay marriage seemed to suggest a marriage between a man and a woman automatically made for the "optimal situation" to raise children.
He added: "However, the reality is that most children in Scotland are not now born to married couples. To insist that being married and heterosexual is best does a great disservice to the large numbers of parents doing a great job of raising their children in loving, stable, but varied, circumstances."
The Barnardo's Scotland director said: "Raising children is about providing emotional security and being a good role model. It is about encouraging good communication and challenging bad behaviour. Children need these things whether their parents are gay or straight, married or unmarried, lone parents or couples."
He said research by the Institute of Fiscal Studies in 2011 found children's development does not appear to be affected by parents' marital status.
"What does have a detrimental effect is growing up in poverty, and I would argue that we might be better to focus on tackling this instead," he said.
South of the Border there have been indications the UK Government would only legalise same-sex civil marriages, a move that would effectively prevent all religious and humanist organisations conducting same-sex marriages.