Just be careful with neutering as sometimes they can get infections in their sutures after the surgery. It is easier to neuter than to spay though. I had one male who came out of neutering like nothing ever happened. He healed up fast and he did extremely well. His neuter was only performed because he had a hernia in his testicles and we were concerned he was in pain from it. On the other side of it, I've read of pet owners having to deal with infections with the sutures, or their chinchillas not eating after surgery. Requiring hand feeding, which sometimes worked, sometimes didn't. Depending on the problem, some chins did survive because their owners acted quickly, some didn't.
If the baby is nursing and the baby's tummy is full, then the mother has milk. If she doesn't have milk, babies can become a little volatile, attacking mom or chasing her around the cage and nipping at her.
Their tails will curl up at the end if they are nursing fine as well, and when they are not receiving milk, their tails tend to lie down flat, bellies do not feel full. If you see the baby lying under the mother for long lengths of time, more than likely she does have milk though.
