Do these do the same thing as arm bands??? I know they're not life jackets and need to be supervised but just wondered if non swimmers can pootle about a swimming pool in them as they can with armbands??? Also all 3 of mine need one (all are 3 and under and non swimmers)and they are sooo expensive don't want to make big mistakes. GLTC sell them but not with free returns so I need to be sure of sizes. The boys will be 4 end of Sep. My daughter 3 end of Dec which sizes would be best???? Would like them to last as long as poss but will be in use a lot June until Sep. Was thinking 4-5 for all 3 but don't want them to be dangerous. Know anybody cheaper than GLTC??? Sorry to sound so dim. New to this swimming lark.