Fiona Onasanya was one of the few MPs to vote against new sex and relationship education regulations in England.
The Peterborough MP was one of 21 MPs to oppose the proposals brought by Education Secretary Damian Hinds which will mean children are taught about different family models from primary school age - including same-sex couples and parents, lesbian, gay, bisexual and transgender identities and the effects of stereotypes about such groups.
The proposals were backed by 538 MPs.
If the regulations are approved by the House of Lords the final guidance is set to be published and come into force from September 2020.
The issue has previously caused deep divisions in some communities, with several schools in Birmingham facing protests from parents over existing LGBT inclusive relationship guidance.
Explaining the reason for her vote, independent MP Ms Onasanya said: “The draft Relationships Education, Relationships and Sex Education and Health Education (England) Regulations 2019 would see pupils taught about relationship education and sex education (as recommended) in primary schools.
“Therefore if schools are to determine the content of sex education at primary school (recommended), I do feel that parents must be provided with detail of how schools plan/propose to tailor these programmes.
“I am not a parent, but understand that age and readiness do not necessarily correlate. How will schools determine which pupils are at the right age and stage for the programmes?”
The new guidance will apply to primary schools as well as secondary schools, but teaching must be “sensitive and age appropriate”.
Faith schools will be permitted to teach the guidance from a “distinctive faith perspective” and a “balanced debate may take place about issues that are seen as contentious,” according to the Department for Education.
It is the first time sex and relationship education guidance has been updated in 20 years.
Conservative MP for North West Cambridgeshire Shailesh Vara voted in favour of the new regulations.