It's pretty classic - the little girl gives her pony a sugar lump. Popular wisdom, though, says sugar is bad for you.
So, is it bad for horses? The jury's out. Some vets say sugar is every bit as bad for horses as it is for us. Others say a lump or two won't hurt.
The general consensus is that sugar lumps and candy (horses enjoy peppermint candy) are not very good for horses - but aren't going to cause huge problems if fed in moderation. Horses already take in a lot of sugar in their natural diet - that sweet tooth is actually how they pick the best grass.
Horses with insulin resistance or cushing's should not be fed sugar. And before giving somebody else's horse a treat, it's best to ask if it's okay first - some horses will bite if offered treats.