The mum - who was four months into her pregnancy at the time of the shocking attack - received blows to her stomach from Peter Lowe, 68, as he tried to snatch her child.
Lowe has now been jailed for two years, with the judge calling him 'every parent's nightmare'.
The sickening events happened in Grimsby in June last year when the unnamed young mum was attempting to put her daughter into her pushchair.
Lowe approached her and punched her on the side of her stomach and tried to take the baby.
The 20-year-old lost her balance and the child fell through her arms. Lowe then tried to grab the baby by her arm, while the mother attempted to cling on to her.
The old man grappled with the woman, squeezing her arms to try and make her lose her hold on her daughter.
The Mail reports that he punched her again causing her to fall to her knees, before trying to make off with her little girl, who was said to be 'screaming and crying out'.
Lowe only ended his attack when a passer-by shouted at him. He ran off, but was later arrested.
Sitting at Grimsby Crown Court Judge David Tremberg told Lowe: "It's every parent's nightmare to have a stranger try to abduct their child, particularly in a case like this when it was a young woman who was on her own and 17 weeks' pregnant, and against whom you used some violence."
The court heard that Lowe had shown remorse and was suffering from mental health difficulties, including schizophrenia.