yes, I think so. I tried to show my 3 year old in hand and he was F/S with cob cheeks. Now 6, he's F/S everything with extrafull browband, although admittedly I do get the cheeks shortened.
Mind you I really hope not much! My yearling is already F/S and has a really fine body , looks totally out of proportion.
Mine hasn't. I bought a new bridle for my AA x WB when she was 3 and it still fits lovely now she's rising 6. I have to buy a cob size bridle but a full size browband & breastplate- very annoying!