Don't take this the wrong way, but is there evidence of this? Just trying to stay clear of possible bias.
http://www.vox.com/2014/7/17/5902177/9-questions-about-the-israel-palestine-conflict-you-were-too
Add to that what you can already read on this and the previous page, that there is no evidence other than the IDF's word that Hamas kidnapped the teenagers.
If you are interested in the story surrounding the beach bombing, watch this NBC report starting at 01:43
http://www.msnbc.com/all-in-with-chris-hayes/watch/four-boys-killed-on-gaza-beach-306364483898
The IDF justified that attack by claiming they were playing near Hamas installations from which rockets were fired, though surprisingly the journalists staying in the hotel next to that beach have not seen any rockets coming from that place. Not to mention they would not stay near that place if it actually did.