I always find the klontalersee very beautiful. Take the A3 to Chur exit 44, watch out for the small sign (before Glarus). Watch out, the lake can only be accessed from this direction as the pragelpass is closed for trafic during the weekends.
About the lake itself, it has very clear bright blue water. It is a very quiet lake (but I since you have baby plans, I don't know whether its quiet enough for that)