If a Children's Zoo Pack were to become a thing, I think these would be my choices for the animal list.
1. African dwarf goat
The only domestic breed of the four habitat species, but this is the most common domestic animal in zoos and is regularly kept in either walkthrough enclosures or ones that allow close access to visitors. They can also be kept with wild African herbivores, including giraffes, zebras and ostriches. They are probably the archetypal children's zoo species.
2. Bar-headed goose
Waterfowl are commonly kept in zoos, and many species are suitable to walk among and feed. The bar-headed goose is the most commonly-kept of any exotic goose species, kept in all manner of different enclosures from walkthroughs and mixed enclosures to ornamental ponds, fountains and moats, are attractive and sociable birds and are also pretty friendly as far as geese go.
3. Black-capped squirrel monkey
Because squirrel monkeys are such active and curious animals, they are often kept in more interactive settings such as walkthrough enclosures and children's zoos (like the new one in San Diego). Unlike the smaller marmosets and tamarins, which live in small groups based around a single breeding pair, the squirrel monkeys live in large groups (up to 100 individuals) with many males and females, so I think they are the ideal small monkey option.
4. European rabbit
An Endangered species native to southwest Europe, this is the ancestor of all domestic rabbits. I would have the wild rabbit in-game, as they would be able to fit into a children's zoo setting but are not limited to it, so would also fit into a European wildlife exhibit or even an Australian exhibit (as Zurich Zoo has done/plans to do). Although most wild rabbits are brown, they do naturally come in a variety of colour morphs including albino, black and ginger, so these colours could be selected for in a children's zoo.
5. Western honeybee
The exhibit species is a semi-domesticated insect, commonly kept in zoos around the world. As well as matching with the farming theme that often occurs with children's zoos, they could be kept nearby to the butterflies or in any Eurasian or African exhibit. I would have the bees be displayed in a naturalistic display based on a hollow tree (like the bee exhibit at Vienna Zoo, pictured below), with a special feature being that the bees have an access tube in one wall of the exhibit, so a visitor path cannot go right up against this wall.
With that, there would be a species from Africa, Asia, South America, Europe and a more general Old World species. None of them would feel out of place if displayed away from a children's zoo, but would make the construction of one much more viable.