Well, it's best to neuter/spay the pups before they mature sexually.
Meaning, bitches before they are 6 months of age (usually done between 4 to 6 months) and males around the same age. I had Chloe spayed at 6.5 months, 2 hours after I got her home she was up and running (and jumping, and jumping..).
If you are not planning on breeding the dog (and even than the dog should have breeding documents) it's best for their health to spay/neuter.
Is Willy going to be neutered? If so, don't worry, it's a relatively easy surgery, and they bounce back within hours.