Having loose stools sometimes is normal for toddlers depending on the toddlers diet but most times the toddler should have more firm stools.
It could just be the diet your child is eating or could be a viral infection or just simply diarrhea and if the child has a normal appetite and is eating properly then it's usually no cause for concern for your toddler to sometimes have loose stools.
If the loose stools continue for a week or more then I would speak with your child's doctor about it to find out what is going on.
But most times it's very normal.
To firm up your toddlers stools though you can put them on the BRAT diet which is Bananas Rice and Toast which can help their stools turn from loose to firm.