By taking the money from Emma he made sure that she grew up with means of obtaining her own money and not
Just have it given to her. If August gave her the money then she would know that Neal still cared for her and she would want to find him.
It’s good to see people on here do have a brain. Not to mention, the last thing you do for your prison pals, especially ones locked up for stealing, is send them money through the mail. They would have been even more suspicious of her, having 20 grand sent to her in the mail. And, we still don’t know if August did indeed steal the money, or maybe he just hid it for her, in case of a rainy day.