[dogsbody70]

This is a story of my brother’s son who is three years old.
One day, his family and I went to shopping together. My brother was looking for a hydroscope for his son, but the shop didn’t have ones for children.
by yuritokoro I think.

I noticed the above item in your message. RE--"But the shop didn't have ones for children." It would be better to write, "the shop did not stock suitable hydroscopes for children."

Or:" but the shop didn't stock any that were suitable for children."

Others have helped you with other examples beautifully.