Offer healthy foods daily, but don't blame yourself and don't stress out about it (easier said than done, I know). Give him a multivitamin like Pentavite and remember, you can only do your best.
I say this because my DS is 14 and was and still is a very fussy eater. I spent years worrying and judging myself about his eating habits; I tried it all, every trick in the book, but I believe some people are just born fussy. It could even be genetic, his dad is extremely fussy.
Anyway, my boy is a picture of health, despite his terrible eating. He's above average academically, excels at sport and hasn't ever had more than a common cold all his life (touch wood).
I always made sure he ate weetbix every morning during childhood and he's an OK meat eater, but will never eat stuff like salad, most vegies and tuna. But he eats plain white fish, carrots and all dairy. He's a very plain eater, loves junk food, too (as most teens do, lol) but I just keep making a home cooked meal every night and adjust his serve to his liking.. I have given up trying to force him to eat his vegies a couple of years ago. He now takes a teenage Men's multi.
There's only so much you can do x
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