Typically, at 3-years-old a child should be producing short phrases or sentences. I would seek out an evaluation through your counties Intermediate Unit or a local speech language clinic. In the mean time, you can work toward improving his speech and language by reducing screen time (TV, tablet, phone, etc.), playing back-and-forth games with him, and talking to him about anything and everything that you or he is doing. Good luck!
I would seek out a speech language evaluation through your daughter's school or a local speech language clinic. They can complete an evaluation to determine what specifically your daughter needs to work on and give you more specific strategies from there.
A typical speech language therapy session can last anywhere from 30 minutes to an hour, typically. Although, it does depend where you are taking her for services. Good luck!
Therapy will be catered toward your mother and her specific deficits at this time. The speech language pathologist she sees will complete an assessment to find out what those deficit areas are. Some examples of what treatment may look like includes: having conversations and answering questions on different topics or various oral motor exercises. It all depends on her specific areas of need. I hope this helps.