Whether or not you are wasting your time depends on the reasons as to why you want to incorporate Spanish in your lessons.
If your reasons are; for the child's benefit, as something fun, interesting, different, and challenging to do, to enrich your program, to stand out from other daycare providers by offering a little more in your program which will hopefully gain more clients for you, etc. then, no, you are not wasting your time.
If your reason is to start the children on a life-long journey of truly speaking Spanish, then, yes, you are wasting your time because most likely they will not speak Spanish again until they are in high school and are forced to take a foreign language. But I don't think that's why you want to have Spanish lessons in your daycare.
Here's my story... ( I always have a story!
) A few years ago, my father was diagnosed with Alzheimer's Disease. I then became concerned about myself developing Alzheimer's and researched the disease. Everyone knows that the brain is a 'use it or lose it' organ. But what I learned from my research is that if you learn foreign languages, whether they are spoken or non-spoken (such as sign language and short-hand for those who are old enough to know what short-hand is
), and even if you only use that language for a very short time, whether for one month when you are 2 years old or one month when you are 80 years old, it will change the way your brain neurons and dendrites grow. If you learn a foreign language and only use it for a short time when you are young, it will help you to have a less change of developing Alzheimer's when you get older!
So, even if a child leaves your daycare after just a few weeks of learning Spanish or whatever other foreign language, spoken or unspoken, and they never use that language again in their life, you have helped that child's brain protect itself from developing Alzheimer's!
So, in my opinion, no matter what your reason for considering teaching Spanish in your daycare, the answer to your question as to whether or not you will be wasting your time, is NO. You will not be wasting your time because you will be helping each child have a better chance at a happier, healthier, and more coherent life in their old age! You will truly be helping each child for the rest of his/her life!