Until a chin is about 6 months old, you really can not tell for sure. You look more at the parents and
hope the kit turns out as good or better. But, the one fault with this is that a chinchilla pair can not produce kits exactly alike everytime ... nor do they produce kits exactly like themselves all the time.
Many years ago, before I knew better ... I put a pair of chins together, that were not as big as you would normally want to have in a breeding pair. Normally this would be a "no-no", but dumb beginners luck ... all but one kit out of 17 has been bigger and better than either of the two parents. I do consider it 'dumb luck' because I did not know what I was doing and it was totally against the laws of average. As a rule, it is better to follow the rules.
Now, on the other hand ... there are some kits that just jump out at you saying "I am beautiful now and I will always be that way!" The little one below is one of "those kits" ... she is almost a year old now and looks every bit as good, if not better, now, than she did then.