Parents with picky toddlers - how can I sneak nutritious foods into meals?

My 2 year old is super picky. She only likes to eat cheese pizza, homemade alphabet soup, mac & cheese, pancakes, crackers, and yogurt. She never tries anything new...she immediately blows it off if she doesn't recognize it. I've even tried to sneak some Pediasure into her milk and she won't drink that. She's needing to gain a little bit of weight too. Does any one have some tricks on how to sneak something healthy into the foods she eats? I've tried putting a can of baby food into the pancake batter (sweet potatoes). Is there anything else I just haven't thought of?! Is it really true that they'll eat anything if they're hungry? Some times I feel like my toddler would rather starve herself than try something different :(.