not “hot” or “cold” is because of the sensitive environment the yeast needs to be in to grow. if it’s too hot it will not work, it’s basically broken… and if it’s too cold then it will not grow because it needs a certain temperature to do that.
depending on how well your toddler can handle the electric mixer, he can help with this process as well. having common sense and knowing your child is asked here, never leave his side and make sure to step in and take over to finish the last part to make sure it is all nicely mixed and there is no flour stuck to the 