I have been using K9 browser on my phone for a long time and just decided to see what else is out there. I found this great app called F-Secure Child Safe ($2.99). Though not free, this is the browser I use now, it lets me hide the address bar for more real estate and has many great features -

  

You will need to set a hard to remember password and also don’t forget to disable your Safari browser in Settings-General-Restrictions.