Two options:
A) Confront him in a friendly and polite way: “dekhein, bache jab mukhtalif baatein sunte hein baron se to confuse hote hein, agar apko lagta hai ke meine koi ghalat faisla kiya hai to mujhse bolein takey mein bhi apni ghalti dekh sakoon”
B) If he is not such a nice guy then I would give an example of someone else who tried to give your kids advise and laugh it off by saying its hilarious how parents with no kids try to interfere and brainwash other peoples’ kids.