I feel that film does drop the F-bomb more frequently than the previous ones.
Here are scenes which I personally chose to cover my 5-year-old's eyes up for:

* In the scene where Cade & Co. have jumped out of the car park in Shane's car and are attacked by Lockdown, Lucas (bearded hippie) fails to escape from the blast which completely incinerates him and leaves a gruesome standing burnt out corpse
* In the fight scene between Optimus Prime and Lockdown -- it ends with Optimus Prime cleaving Lockdown in half

And I found that my daughter was particularly scared when:
* When Cemetery Wind (the taskforce) come onto Cade's property and attack Cade & Tessa
* When Tessa is getting out of the car inside Lockdown's ship, and she's attacked by those oogly-eyed drone-bots and has to kick them away
* Any scene where the Steeljaws (cybernetic wolf-like creatures) appear
* The close-quarter fight between Cade and Savoy (Cemetery Wind commander) inside the flat in Hong Kong.

I let my daughter bring Slumblebee along and told her to hug him extra tight if she got scared, and both my wife and I were sitting on either side of her, so she hugged onto either of us as well.