The first edition of the Tales came out in 1807, and it seems to have been reprinted several times since. There are several editions available online, including multiple copies at Project Gutenberg. If you'd rather have a scanned version of an illustrated book, the University of Florida Digital Collections can oblige you.
In searching for an online preface to link to, I found that minor variations seem to pop up. This version seems close to the one I have, without the typo in the last paragraph that mars mine. I suggest reading the whole thing, but here's the last half, to whet your appetite:
Add this to the evidence that we tend to set our sights lower these days. These tales for 'very young readers' are not dumbed down in the least.
It has been wished to make these Tales easy reading for very young children. To the utmost of their ability the writers have constantly kept this in mind; but the subjects of most of them made this a very difficult task. It was no easy matter to give the histories of men and women in terms familiar to the apprehension of a very young mind. For young ladies too, it has been the intention chiefly to write; because boys being generally permitted the use of their fathers' libraries at a much earlier age than girls are, they frequently have the best scenes of Shakespeare by heart, before their sisters are permitted to look into this manly book; and, therefore, instead of recommending these Tales to the perusal of young gentlemen who can read them so much better in the originals, their kind assistance is rather requested in explaining to their sisters such parts as are hardest for them to understand: and when they have helped them to get over the difficulties, then perhaps they will read to them (carefully selecting what is proper for a young sister's ear) some passage which has pleased them in one of these stories, in the very words of the scene from which it is taken; and it is hoped they will find that the beautiful extracts, the select passages, they may choose to give their sisters in this way will be much better relished and understood from their having some notion of the general story from one of these imperfect abridgements; - which if they be fortunately so done as to prove delightful to any of the young readers, it is hoped that no worse effect will result than to make them wish themselves a little older, that they may be allowed to read the Plays at full length (such a wish will be neither peevish nor irrational). When time and leave of judicious friends shall put them into their hands, they will discover in such of them as are here abridged (not to mention almost as many more, which are left untouched) many surprising events and turns of fortune, which for their infinite variety could not be contained in this little book, besides a world of sprightly and cheerful characters, both men and women, the humour of which it was feared would be lost if it were attempted to reduce the length of them.
What these Tales shall have been to the young readers, that and much more it is the writers' wish that the true Plays of Shakespeare may prove to them in older years - enrichers of the fancy, strengtheners of virtue, a withdrawing from all selfish and mercenary thoughts, a lesson of all sweet and honourable thoughts and actions, to teach courtesy, benignity, generosity, humanity: for of examples, teaching these virtues, his pages are full.
And, please note, in the above preface, brothers are expected to watch out for their sisters. If you are a feminist, I'd invite you to stop having a hissy fit long enough to think about the alternatives. Do we really want to encourage boys to not look out for their sisters? I don't think so. Admittedly, loving protectiveness can be overdone, but kept in check it's a wonderful quality, I think.
A side note. In my copy, Shakespeare is spelled Shakspeare.
Links to some earlier 'children and Shakespeare' posts here.