Found this on a quick Google search:
Step 1
Place a piece of ice in the cloth or wear gloves to hold the ice (to protect your fingers) on the gum. This will make the gum harden.
Step 2
Gently pull off the gum from the car seat. If pulling gets you nowhere, use a blunt scraper to scrape it off. If the gum gets soft again while you are scraping, reapply the ice until the gum hardens.
Step 3
Spray WD-40 on the remaining areas of gum.
Step 4
Scrape off the rest of the gum. Blot the area with a paper towel to remove excess WD-40.
Step 5
Spray upholstery cleaner on the seat. Scrub it in with a soft cloth towel. Then wet a sponge with warm water and scrub the seat to remove the upholstery cleaner, leftover traces of WD-40 and any remaining particles of gum. Allow the seat to dry completely.
Would suggest you try a section of seat that cannot be seen with the WD40 before you start JUST IN CASE.......