What sort of baby do you want them to have?
The r-selected type of creature which other answers have mentioned (small with large litter size), tend to give birth to helpless babies which cannot do anything for themselves. Blue tit chicks, kittens and mouse pups, for example, which are blind at birth, can't walk, can't find their own food, and so on. These are termed altricial offspring
Exception: animals which have no parental care, like insects. Fly maggots and butterfly caterpillars are from large litters but can look after themselves from the moment they hatch.
The K-selected creatures (big with small litter size) tend to give birth to well developed babies which can walk within minutes or hours and can run/swim at full speed within a day, to keep pace with mum. A caribou calf or a dolphin calf, for instance. In species which don't feed on milk, the baby can also feed itself. So a hen or duck shows her babies what is edible, but doesn't collect food for them. These babies are termed precocial.
Exception: being a prey species will tend to drive you in this direction as soon as your body size is too big to hide your babies in burrows. Baby has to be able to escape the snapping jaws of the carnivores! However wild boar still have large litters
Extremely Notable Exception: human beings. We are a big K selected creature with a helpless baby. Human babies don't even learn to crawl for several months after birth. Compared to chimp babies, they are hopelessly underdeveloped. This contradiction is evolution in action - becoming bipedal and big-brained has forced a helpless baby on humanity as a compromise.
Soooo... if you want creatures which are just humans with the serial numbers filed off, make them big creatures with small litters of helpless babies.
However, if you want them to be a more 'typical' big mammal, they'll have small litters of well developed babies. In human terms, they'll give birth to a child which is as large and active as a toddler.