I don't see any point in buying expensive gear for young kids for example they grow... and very quickly too
a cheap wet suit would do and most shops in Cornwall .. if you ever go there, do buy them back from you if you buy another one off them. Hats off to them
at 4 yr old I can't see you taking a him out in rough
weather so a decent fleece and a waterproof mac kept in a dry bag should suffice
If you are loaded though ignore the above and get the best