
Hi Olivia,
Little boys and little girls are human terms - at 5 months old, your "little boy dog" could well already be fertile - despite the fact he is still simply a young puppy. Add a "little girl dog" - otherwise a bitch puppy, and at a similar age in a toy breed she too could be fertile :( In other words you would have two young puppies potentially able to produce puppies - not that the mother or the litter would be likely to survive the experience - so I'd strongly recommend you forget this idea for now.
Please let your male puppy mature until around 18 months of age at least before adding another puppy to your household. This will give you and him proper time to establish a good bond and countermand any training issues. Then if he is a happy, sociable, and completely well behaved dog you could consider buying another puppy although by that stage you may find that you don't really want to go through all the hassle again so quickly ;) Regards, Teri