That's totally normal for that age. The important thing is to never give in. My 2nd son was my worst about that...I mean TERRIBLE, but our pediatrician told us not to give in and to only offer good healthy foods and whatever everyone else was eating. She said that if he got hungry enough he'd finally give in and eat what was given to him. I was especially concerned with him because he was already very small and his weight was very low as it was and he was having to drink pediasure/carnation breakfast every morning, but like you, I didn't want one of those kids that only at Mac'n'Cheese or chicken nuggets all of the time (All he wanted at that age, though was crackers and bread). Eventually (It took a few weeks) he started eating well. He was still a fairly picky eater until he was about 3, but he did get to where he'd eat, maybe not a lot, but enough (a toddler's stomach is only as big as their fist, so they don't need much food to begin with). By the time he was 3, he BEGGED for carrots, broccoli, chicken and all of the good foods. I had picky eating toddlers with #1 & #2. My #3 has always been a piggy and will eat anything and everything in front of him. His problem is always keeping him from eating TOO much. :)
If you're concerned about nutrients, just give him a cup of carnation breakfast for breakfast every morning (the same as pediasure and a WHOLE lot cheaper) until he starts eating well. He's definitely too old to be fed, so make sure anything you give him he can eat himself. He should be eating everything you and your husband eats. Trust me, it's better to never let them know (even as little as he is) that there's any other option other than what everyone else is eating. You don't want him to be one of this kids demanding something different every meal other than what you've already fixed (My husband was raised that way and I had to break him out of it at almost 30yrs old and his niece is the exact same way, everyone has always had to make sure they have ramen noodles and/or mac'n'cheese at every meal she's at and she's 16yrs old now, but that's still just about all she'll eat).
Good Luck!
K.
SAHM of 4 (9mths, 3, 5, & 6)