Yes. They will have to input passwords to access the wifi (assuming you have a password on your home wifi) or anybody else that has it (some businesses have it but you need a password to connect, many public places offer it free), sometimes their schools may even make it available (but limit what they are able to access through it, for example, no FB).
I'm not familiar with Freedom POP, but I'm assuming it is a prepaid type thing. If it isn't, and you are under a contract for a certain amount of time and you *can* can over on your data usage, make sure you talk to someone who knows how to set the phones so that they aren't using much data. It doesn't take long to hit 500mb, especially if they are watching movies/YouTube! And kids are less likely to be aware of how much they have blown thru... you could get hit with a huge bill for data overages. (but, if it is a pre-paid phone, then I don't think that can happen, they'll use their data up and that'll be it until the next time you buy it, I think... )
We have had 3 smartphones for the last 6 months. 3GB of date available. We came close to going over a month ago b/c of some wifi outages (DSL line problems) at home, but I get notices on my phone from Verizon when we hit certain usage points, and I just told the kids to cut it all out except mssgs (which doesn't use any, but you have to have it on to send/receive pics for some reason).
Husband now has a smartphone as well, but I set it so that he can't use data for much of anything... since he doesn't know what he's doing and could just randomly hit something and use a lot without even knowing. Or knowing what he did or how to stop it.
We'll see how we do. On average, we rarely go over 2 GB with the 3 of us. Will have to see how husband's use impacts that.
But yes, set the phone to automatically default to wifi when it is available. That will save you tons of data use.