MP stands with son on same-sex marriage

Susan Lamb was a teenage mum.

And the new Labor MP admits walking into federal parliament house for the first time sparked the same feelings.

"I was incredibly nervous, more than a little overwhelmed and I had a great sense of responsibility on my shoulders," she says.

The Queensland MP focused much of Monday's first speech to parliament on family - to her father who was injured at work and her four sons.

And she used one of her boys to illustrate her strong support for same-sex marriage.

"Those of us who are parents understand the innate instinct to fight against the unfair treatment of our children," she said through tears.

"I carry a sense of disillusionment that our laws treat the love of one son inferior to that of his brothers.

"I stand in solidarity with my son and the LGBTI community."

A Turnbull government plan for a plebiscite on same-sex marriage was deeply offensive to LGBTI Australians, she said.

Discrimination against vulnerable minorities should never be up for national debate.

After taking over from her predecessor Wyatt Roy at the July election, Ms Lamb wrote a letter to each of her sons.

"I explained I'd be likely to miss some football games, I'd not be there as often to help them so much with homework and I'd frequently repeat the same questions," she said.

But she told them the possibility of shaping their future, and the futures of other, drives her as a politician.

Ms Lamb also thanked Mr Roy, 26, for proving that age was no barrier to serving the community.