Is it possible to read to multiple toddlers at once?

You could try telling them ghost stories, as that's a group activity, if you don't mind having a household full of scared to death toddlers in the end. :)

But seriously, no sorry the read to (toddler, child) interactions are programmed to be one on one. A mod that allowed this to be a group activity would have to rescript and reanimate the entire thing from scratch and I've never seen one that did that.