Gary Walter had put £10 on a 13-game accumulator bet using a mobile app.
But the 24-year-old's son Archie managed to press the cash-out button while his was playing with the phone.
Although he'd already guessed three results correctly, the option, that allows betters to close a bet early, meant he only received £7.
Sadly, the rest of his game predictions came in correctly as well, meaning he would have won an amazing £49,435.34!
How cross would you have been?!
Gary, a car worker from Birmingham, said: "I was strapping Archie into his car seat and I'd left my phone on his lap. The yellow button on the Bet354 must be very attractive as he pressed it.
"This would have paid for our wedding and deposit on a house. I can't wait to tell Archie when he's older."
For exclusive competitions and amazing prizes visit Reveal's Facebook page NOW!