Foster posted a pic of herself cradling her little boy in the hospital on Thursday.
"My favorite 5-year-old. What a blessing!" she wrote. "I have always loved and appreciated my sons but tragedies and close calls make this even more evident."
She also revealed earlier in the day that Cinco was "resting well" and that they'd "had a SpongeBob marathon ALLL night," because "he wouldn't go to sleep!"
Usher released a statement Wednesday night thanking "the two men who saved my son's life" after he got his arm stuck in a pool drain while trying to retrieve a toy in the pool at his father's Atlanta home on Monday.
The Voice judge has primary custody of his two children with Foster, but she reportedly filed a request for an emergency custody hearing on Tuesday.
"Now that it's sunk in, she is livid," a source close to Foster told PEOPLE. "Usher has custody and won't let Tameka have the kids, even when he's out of town. She feels like the kids are being raised by his family or by nannies, when they should be with their mother."
My favorite 5 year old. What a blessing! I have always loved and appreciated my sons but tragedies and… http://t.co/hcNDFwJ1Hn— Tameka J Raymond (@TamekaRaymond) August 8, 2013