going in this direction myself, verizon has a prepaid option also its called page plus, everything I have read says you cant go wrong with the no contract options, best part is if you do not like the service just move to another carrier, im going to try T-Mobile, they have a plan that has unlimited txt and Data up to 5 GB and 100 min for 30 bucks, I dont talk on the phone really, if I need to I have a work phone, also you can look into google talk I hear that is pretty neat.
you can get unlocked GSM phones off ebay, that is what you want, so if you decide to get a different phone you just take the sim out and put in another phone, also check out GPP sim if you have a cdma IPHONE it lets you use it on a GSM network, no unlocking required or jailbrake.
Good luck hope you get something that works for your family.