generally they would be formed to be honest, though there are always varying ‘shades of gray’ as they say. Some issues that can raise their head around loose stools include things like gluten intolerance (though tends to be associated with issues in maintaining weight) and lactose intolerance. Both are reasonably simply to check, lactose in particular can be done via a breath test. Gluten is a little trickier but you can look into it by visiting your GP. They may also do a stool test to check for bacteria or similar, all quite standard.
Personally, if your toddler is overly hungry or has issues with weight (either way) I would look into it sooner than later. It may well be absolutely normal, but it’s good to know either way.
Hope that helps