Just As Easy [as taking candy from a baby]—illustration from an advertisement for The L. G. Shell Co., Inc., published in the Roanoke Rapids Herald (Roanoke Rapids, North Carolina) of Friday 22^nd October 1915:

The American-English phrase like taking, or like stealing, candy from a baby means very easy to accomplish, sometimes with an implication of unscrupulousness—synonym: like shooting fish in a barrel.

The earliest instance that I have found is from A Dead Easy Mark, an article about a baseball match between Columbus and Mobile published in the Columbus Daily Enquirer-Sun (Columbus, Georgia) of Thursday 11^th June 1896:

Folk also fielded and batted well. Columbus has, without a doubt, drawn a prize in this player. He is tricky too, and made Mobile give up one run yesterday in the ninth inning that seemed like taking candy from a baby.

The second-earliest instance that I have found is from the following self-advertising article published in The Dallas Morning News (Dallas, Texas) of Sunday 28^th February 1897:

The Whistler.

“You have heard,” said a youth to his sweetheart, who stood,
While he sat on a corn-sheaf at daylight’s decline—
“You have heard of the Danish boy’s whistle of wood:
I wish that Danish boy’s whistle were mine.”

“And what would you do with it? Tell me,” she said,
While an arch smile played over her beautiful face.
“I would blow it,” he answered, “and then my fair maid
Would fly to my side, and would there take her place.”

“Is that all you wish it for? That may be yours
Without any magic,” the fair maiden cried;
“A favor so slight, one’s good nature secures;”
And she playfully seated herself by his side.

“I would fain blow again,” said the youth, “and the charm
Would work so that not even modesty’s cheek
Would be able to keep from my neck your fair arm.”
She smiled as she laid her fair arm round his neck.

“Yet once more would I blow and the music divine
Would bring me a third time an exquisite bliss:
You would lay your fair cheek to this brown one of mine,
And your lips, stealing past it, would give me a kiss.”

The maiden laughed out in her innocent glee,
“What a fool of yourself with your whistle you’d made:
For only consider how silly ’twould be,
To sit there and whistle for what you might take!”

This youth represents a large number of good, honest people, who are either too timid or too inexperienced to secure a good thing that is almost within their grasp. To take a kiss from this lovely maid would have been as easy as taking candy from a baby, but the timid boy was afraid to venture. “Faint heart never won fair woman.”
We see all around us, every day of our lives, dozens of people missing good opportunities to obtain something they want, and which oftentimes they could obtain as easily as the young man could have obtained a kiss from his pretty sweetheart: but they just don’t seem to know how to go about it. To illustrate:
Mr. Thompson is anxious to buy a good second hand surrey. Mr. Johnson, living in the same neighborhood, town or city, has a good surrey to sell, but Mr. Thompson doesn’t know it. Neither does Mr. Johnson know of Mr. Thompson’s desire to buy one. Mr. T., however, has noticed that a great many intelligent people advertise their wants; so he comes down to the office of The News and has this ad. run three times under “Miscellaneous Wants.” “SURREY—Who has a good second-hand surrey to sell cheap for cash?
                                                                      “Address Box M— News office.”
This ad. occupied three lines and three insertions cost only one dollar. Mr. Thompson received seventeen answers in reply, Mr. Johnson’s among them, and as Mr. J.’s vehicle suits him best he buys it at a bargain. Who will say that Mr. Thompson did not make a fine investment when he paid a dollar for that classified ad.? Indeed, the classified ad. columns of The News often seem to possess as much magic power as the Danish boy’s whistle or Aladdin’s wonderful lamp, in procuring just the thing the advertiser wants. Yet there is no magic about them: they are just plain, every-day, philosophical business transactions, based on true business ideas and experience. That’s all.