We use Motorola 250 FSR radios in the parks and they work great.
When choosing FRS radios be sure to get the privacy codes also known as coded squelch. With them finding a combination of channel and code that is fairly quiet is possible, even when there are a lot of radios there.
Using some radio etiquette helps everyone. When calling someone to start an exchange say who you are calling and who you are.
You off the ride yet? vs.
Bob, Sally here, are you off Space Mountain yet?
In the first Bob doesnt know he is being called or who called. In the second Bob knows the call is for him and to reply to Sally. Anyone else on the same channel / code knows it isnt their family.
Turning them off in shows and quite rides keeps you from getting a disturbing call on the channel / code you are using.
The radios are a big help with kids. Think - one need to use the potty - the rest of the clan keeps moving and you use the radio to get back together.
Also in Downtown Disney - dad, one radio and the boy go to the
Lego store mom and the girls shop. Dad and the boys go to McDonalds for a coke and fries, eventualy dad and the boys get too bored and call mom on the radio to go back to the hotel.