The average cold lasts 2-3 weeks, with the worst symptoms occurring in the first 5-7 days.
There is no treatment that changes this and makes a cold go away sooner. To make your child more comfortable, push fluids (preferably water and juice), run a vaporizer and encourage them to rest. Use Acetaminophen or Ibuprofen for body aches, but not for fever below 103. Call if you have questions.