I have 3 different Roku set up under one account, but with my kids if it is not something in there age range I want them to be blocked . is there anyway I can get only there Roku device set up like that? I dont want it to have interference with my device
Sorry, those settings are for the Roku ACCOUNT, not the Roku DEVICE. Likewise the channel list is with the account, not the device -- add or remove on one device and it affects all Rokus attached to the same account. The only thing you can change in the individual device is the order of the channels in the channel grid.
The only way to have different setups is to have separate accounts, keyed to different email addresses. On the kids' unit, you'd need to do a factory reset (Settings > System > Advanced system settings > Factory reset) and set it up from scratch, connecting to the other account. When logged into this account via https://my.roku.com, I'd strongly suggest setting up a PIN and choosing an appropriate option on when it should be required (in fact, I'd suggest doing this on the main account too, at least requiring the PIN to make a purchase). While in there you can also set a parental control option as to the program ratings that can be viewed, but be aware this affects The Roku Channel only -- limitations on other channels must be set with those channels when they provide that option.
Also note that any paid premium subscriptions you have through Roku on your current account will not be accessible on the new account. For a paid subscription to be available on multiple accounts (and other platforms, like computers, phones, and tablets) you must take out the subscription directly with the channel on its website.