A mum has admitted her baby nearly drowned in the bath when she turned her back for less than 30 seconds.

Australian Siobhan Rennie is now warning other parents to be more alert to the dangers than she was – and not make the same mistake of leaving an older child to look after a younger one.

She shared the tale on her parenting blog MeOhMy – claiming it was “the hardest post” she had ever written – and even claimed she felt like “a horrible mum".

The drama began when Siobhan, 36, put two-year-old son Harry and daughter Aoife in the bath together and then suddenly remembered she had to put the washing away.

The tearful mum posted online explaining: “I went around the corner just a few metres to hang up one of my husband’s shirts.

"I didn’t hear anything out of the ordinary, just a tiny bit of splashing.

“I went back to the bathroom maybe 15-30 seconds later (I really have no idea, it was very quick) and Aoife was under water flailing around.

“Harry was laughing. I grabbed her so fast out of that bath and held her to me… she was coughing and screaming.

“Harry suddenly realised she wasn’t playing and his face fell.”

Siobhan said Aoife (thought to be around a year old) is okay – having “coughed briefly” and cried "for a little bit” – but she knows it could have been far worse.

She added: “What I did was completely unacceptable.

“There is NO WAY I should have left them in there together alone. I got complacent.”

“This is the hardest post I’ve ever shared. Even harder than admitting I had PND and anxiety. Because many of you out there will be thinking I’m a bad mum. You’d never do it, right?”

She also admitted she was “stupid” to believe her son was old enough to look after his sister.

“The only reason I’m writing this is because I want to warn you – DO NOT ever think that your baby, no matter how old, is safe in the bath by themselves or with a sibling, even for a couple of seconds.

“I’m sure many people out there will be judging me right now. And wanting to troll me. Go for it. Nothing you can say will make me feel worse than I already do.

“I hate myself. My babies are my world and I will feel guilty about this for the rest of my life – and I’m not exaggerating.

“Please, heed my warning and never take your eyes off them. It could turn out to be your worst nightmare.”

Siobhan has shared post on her Instagram page to her more than 30,000 followers.

Some people thanked her for her advice – while other criticised her for leaving the boy in charge of the girl in the first place.