Why on earth did she let them out into such a dangerous place as the Sand Zone anyway?
Let's see here:
Kakeru:
Jenka's pet. Adores bones and has buried them in countless places, most of which are by now forgotten.
I guess that since he/she likes burying bones, he/she had to go outside to do it, and got carried away.
Nene:
Jenka's pet. Spends most of her time asleep, but her dreams have been known to portend the future.
I'm not sure.
Mick:
Jenka's pet. Loves treasure-hunting. Or treasure *chests*, rather, and recently has taken up sleeping in them.
I guess he went treasure chest hunting, which explains why we find him in one.
Shinobu:
Jenka's pet. Loves dark places. Due to poor eyesight, he roams the darkness using his wild instincts alone.
My guess is that he wanted a change of pace, and went somewhere dark, or got lost in Jenka's house due to poor eyesight, stumbled upon the dark place where we find him, and took refuge by staying there since dark places are his area of expertise.
Hajime:
Jenka's pet and leader of the dogs. While searching for his brothers, he got lost and was taken in by Curly.
Well that's obvious, isn't it? He got lost because he was looking for the other lost puppies.
Also, I'm one of two youthful owners of what used to be a two-month old puppy, and even when I had a fit sibling to be the other main owner, managing the puppy was still very exhausting. Imagine a frail old woman whose magical powers have ceased managing five puppies on her own. I'm almost not surprised they got lost.