A petition calling on state and territory ministers to change Australian gun laws after two teenagers were murdered by their father, John Edwards, in West Pennant Hills, has garnered almost 10,000 signatures.

Mr Edwards managed to get a gun legally while he was in a family court battle for custody of his two children.

If the law required police to notify his estranged partner before approving his gun licence, then the shooting of Jack and Jennifer Edwards may have been prevented, director of Gun Control Australia (GCA) Samantha Lee said.

"Current gun laws fail to adequately protect women and children from gun violence because the law requires an AVO to be in place or a charge for a criminal offence before a firearm can be revoked or suspended," Ms Lee said.