Amenadiel and Linda's baby boy has been through a lot in a short period but now he's dealing with some identity issues that he's not even old enough to understand. In the finale of season five's part one, Charlie gets sick with a common cold like a human child and when his father freaks out, he gets frozen in time like every other human. According to Michael, this is an obvious sign that Charlie is a mortal, which means he doesn't have a lack of vulnerabilities like his father's side of the family benefits from. Understandably, Amenadiel is distressed at the idea that his son has none of the safety rails he would have as a half celestial and Michael uses that fear to manipulate his brother.
But, if we remember Amenadiel's experience in season four, this doesn't quite track. The angel was visited by his sister Ramiel who sensed the presence of a new celestial, which means that Charlie was able to ping her angel alert, so the baby is definitely packing some grace like his daddy. Lucifer suggests that Michael is lying to Amenadiel and made Charlie sick himself, which is also a fair assumption. After all, how did Michael even know Charlie was sick and to find Amenadiel in the hospital? My theory is that Charlie is half angel, but isn't completely immune to human ailments. He's not fully an angel and he's just a baby, after all, it's not like he'll get the full benefits of all that glory.