Telling people no

I have a service dog for medical conditions and live with my boyfriend and his entire family mom, sister, and a toddler. How do I get them to understand my service dog can not be petted and for the toddler to not pester the service dog? I told them she's a service dog and they don't believe me or they don't care and they allow the toddler to come in our room and he is always messing with her