Garner, who is married to Ben Affleck, gave birth to her third child Samuel in February. Witherspoon and husband Jim Toth welcomed son Tennessee into the world in September this year.
"Both of them have a serious sweet tooth. So whenever Reese wants to reach for a chocolate bar she calls Jen instead and vice versa," reports femalefirst.co.uk.
Both of them live in the same neighbourhood and attend Pilates classes together. Witherspoon recently admitted she had been finding it hard to shed her baby weight.