"When I went to check on him, he was not breathing. We are living a nightmare, and I'm dying inside. Please pray for my baby. This can't be real," she wrote on Instagram.
Crew was rushed to hospital where doctors stabilised him with a ventilator.
"This kind of thing only happens to 'other' people. Not me," she wrote.
"Please continue to pray. Please. I don't think I can go on without him," she posted while Crew was still in hospital.
Leach kept her followers updated on her son's condition.
"Crew's tiny earthly body is still with us, although I know he's already dancing and playing in Heaven," she wrote at one point during the ordeal.
"We have some hard decisions to make over the next 12 hours, that no parent should ever have to make."
"We need prayer now, more than before, specifically prayers for peace and clarity on the decisions that have to be made, and for our hearts, the pain is unbearable," she added.
"I keep thinking that I will wake up from this nightmare, but I don't."
The heartbroken family is now saying a final goodbye to Crew.
"We are making hand and footprint imprints, a family handprint tree and a fingerprint charm," she wrote.
"Jeff and I take turns being strong for each other, and our kids have been so strong. We are just taking things, minute by minute, hour by hour, although it feels like a daze."
She has thanked her friends, family and followers for their support and prayers.
"Hearing a baby cry. Seeing a baby his age. Shopping Nordstrom for the dress I'll wear to my son's funeral," she wrote.
"It's all too much. I'm sorry to vent, but this is my heart. And I need all the prayers to get through this."
