Instagram users have spotted the serious problem with this accidentally rude advert which asks men to become "members".

WonderDads is a California-based organisation of fathers which offers membership perks and a magazine, provides inspiration for activities to do with children and helps men plan a "Dad-Kids trip" or a bucket list.

The company says: "WonderDads helps busy Dads embrace their kid's childhood."

But the advert, which was spotted as a sponsored post on Instagram, does not quite convey the same wholesome message. In the silhouette image, a father is dressed as a cape-wearing superhero with his hand holding a heart towards his two children. Unfortunately, because of the position of the hand and the lack of definition in the picture, it looks more he is pointing his penis instead.

Cartoonist Kris Straub shared a screenshot of it on Twitter, saying: "Hey artists, silhouette clarity is important."

Because the text is centred on Valentine's Day, one wit took the innuendo further by describing it as a "heart on".

Another Twitter user said that both children were "clearly staring at dad's mighty 'D' sword".

Others wrote "no" over and over again.

A WonderDads spokesperson said: "We're a company of dads. In our entire history as dads, and as a company, this is the one time our 'heart' wasn't in the right place. It was a genuine mistake."