Original: Dingoes leave small prey near the den to their pups.
Corrected: Dingoes leave small prey near the den for their pups.
Short, simple explanation for a 5-year-old:
- Who? Dingoes — the animals.
- What? leave — they put something down.
- What do they leave? small prey — this means small animals (you can say "small animals" to make it easier).
- Where? near the den — by their home.
- For whom? for their pups — this means it is meant for the baby dingoes to eat.
So an even simpler sentence you can say: Dingoes leave small animals near their den for their pups.