I’m wondering if anyone knows how to make a kid’s voice sound like a adult’s voice and a adult’s voice sound like a child’s voice. Hopefully someone knows, please help.
A “little” bit of pitch change can help (higher for female or young person), but that will not change the basic character of your voice. There are many other things that make up the character of a voice including vocabulary, accent, resonance, expressiveness, emphasis, and so on.
Have you tried Rovee http://www.g200kg.com/en/software/rovee.html which is a VoiceChanger / formant tweaking VST effect plug-in with presets for “converting” voices to male, female, toys or robotic? Don’t expect miracles but it works quite well in Audacity.
See here for how to install VST plug-ins http://manual.audacityteam.org/o/man/faq_installation_and_plug_ins.html#vst_install .