Each family member will have to complete their own DS-160 form.
However, 6 year old is exempted from making personal appearance at the consulate. Both parents can appear and carry child’s passport.
First schedule your H-1 interview and at the end of the process it will ask if you need to convert it to a family application. There you can include your dependents and everyone (w/ or w/o kid) can appear together. You should do this once amendment has been approved.