The boy is just 7 months old, with a rare condition.
Now doctors desperately want blood samples from the father, to perhaps help is son's treatment.
With his 7-month-old in his hand and his girlfriend by his side, Carlos Oliva Guillen walked out of the Elizabeth Detention Center with his imminent deportation to Honduras halted.
"I feel good," the 26-year-old said, "You know, truthfully, I really didn't expect this. It's a blessing to be reunited here with everyone."
Authorities released the undocumented immigrant following pleas to politicians, pleas that centered on the healthcare needs of his young son, who suffers from a rare type of low blood sugar.
Doctors treating little Jen-Carlo urgently need a sample of his father's blood.
"I was there with my son and I didn't know exactly what to do, the support that I had. My boyfriend was my main support, going to college, pushing me to go to finish school. He knew I had a future," said Emily Navas, Jen Carlo's mother.
Guillen, a construction worker who has been in the U.S. for 10 years, will have his immigration case reopened and re-examined.
In the meantime, he hopes his blood will pave the way for his son's medical treatment.