Jonathan Mastalerz, to his mother,
Chelsey Reep, printed on the front and back.
"Me and dad were talking. We think we should all have the same last name," the front message read.
The back of the baby's onesie read: "Mommy, will you marry daddy?"
Video of the proposal shows an overjoyed Chelsey holding baby Maverick and reading the front of the onesie before Johnathan drops to his knee and opened the ring box to show the wedding ring.
Chelsey wiped away a tear as she said, "Yes" to the proposal in the video.
UMass Memorial also shared photos of the baby wearing the special message onesie and resting the ring box on his stomach while napping, as well as a photo with his parents as he's fast asleep in his father's arms on Monday (August 2).