"Jennifer told her pal that the difference between having two kids and three is 'massive,' and said Sam would complete their family,” the source told Radar.
"In fact, Jen admits she and Ben had only planned on having two children, and Sam was a wonderful but genuinely true accident.
"They love their kids, but she’s really had her hands full with three since Sam was born in 2012 and while things are starting to settle down, it’s been pretty exhausting, especially with Ben being so busy."
In September 2012, after having Sam, Garner told Ellen Degeneres; that they weren't looking to have anymore kids.
"There are 57 kinds of contraceptives used pretty much," she joked.
But seriously, Garner added, "I think we have provided the world with enough children."
According to the source, Garner is proud of her man winning the best picture Oscar for Argo in 2013 "and wouldn’t change a thing, but it’s been tough on the hands-on mom.
"They’re both looking forward to some couple’s time this summer and are planning a kids-free vacation for just the two of them. She needs it."