To talk or not to talk

My almost 16 month old baby boy doesn’t seem to want to speak. He can say Mama and he has said dada but won’t say anything else. I’m encouraging him everyday to be able to speak eg. saying to him when he wants a toy “car please” “tar” but still nothing! I’m starting to worry as by this age my little girl, who is almost 6, could say “tar” “please” “mama” “dada” plus a lot more.

He understands exactly what I’m saying, he’s intelligent but just doesn’t want to seem to want to talk. It’s a task getting him to say mama and he certainly doesn’t want to say dada anymore. Is anyone else going through this? Any tips? Am I to worry?