Will using toys desensitize the Vagina/Clitoris

Toys or regular stimulation do not desensitize the body, It's actually not possible to desensitize the body unless a hormone/health issue or damage to the nerve endings.
What is good to remember is that a Vibrating toy will allow the deeper nerve endings to be stimulated more: a non vibrating object (finger, P3n!s, tongue etc) cannot stimulate the body as much because they can't send vibrations through the body like a toy can.
This means that most women will orgasm more with a toy because of the vibration and they can put it exactly where it feels good - not the fact that they orgasm less with a partner.
Finding that sexual connection is different with each partner and it can take time and some fun exploring together to work out what is best for you both.
Foreplay and massage is key here and a perfect place to start.
Always use a good lubricant to increase pleausre and other enhancement products as these are there to heighten your body more.