Depending on what qualifies as struggling to survive, about 30 is an army infantry platoon, three squads of ten men plus a platoon leader, platoon sergeant, and maybe a radioman/driver for the platoon leader. Not always up to full strength, but combat experience has driven decisions on unit size.
And that amount is a largely unworkable number in fiction--even for an author who includes hundreds of characters in his stories.
Ideally, a core group of characters will range from 5 (best) to 10 (weaker), otherwise readers will continually be scratching their heads, wondering who is who--especially if a posting takes longer than a week. Even though I posted twice a week, my fans would typically reread the previous chapter so they could remember what was happening from one chapter to the next. Adding that many characters make a story unmanageable.
Not knowing where your next meal will come from or when. living on the edge of starvation, not for a few days, or even a few weeks, but for months with no end in sight because you lack the necessary skills to survive without modern infrastructure.
A basic premise of most PA stories (zombie apocalypses included), is that there's a wide variety of leftover food in stores, people homes and warehouses that's simply there for the taking. Thus scrounging for meals isn't as tough as if the kids were dumped in the middle of an isolated forest.
Generally, survivors in most stories move from the security of one house they can defend to another, minimizing the amount of time they remain in the open.
Also, one of my pet-peeves about PA stories is that they fly in the face of most real-life experiences. According to the collected wisdom of most PA stories, civilization collapses within days without the constant rule of the government. But in most widespread disasters, where the government is unable to reach anyone for weeks or even longer, most people pull together, helping each other rather than fighting tooth and nail. Thus the entire premise of most of these stories falls apart. They are not reality-based stories, but pure fantasy about how essential the rule of law is to human society. If a government collapses, another steps into it's place. In most places where this principal fails, it's because the government refuses to back off once it's lost control, becoming worse than the people working to upset them.
Still, PA stories are fun, no matter how ridiculous they are, so I think I 'll keep reading them.