You can change the Gender and age using StartVoice(VoiceGender gender, VoiceAge age)
Simple Example:
PromptBuilder pb = new PromptBuilder();
pb.StartVoice(VoiceGender.Male, VoiceAge.Child);
pb.AppendText("I like my toy car");
pb.EndVoice();
You might want to search for TTS's that support your desired picth.
Here is the link for all languages available: Languages
Cheers