My youngest son can go through phases of eating like a horse and hardly eating enough to keep a flea alive. We can never be sure which food mood he'll be in and have got used to how he is - he's not picky and will eat, pretty much, anything but sometimes he just doesn't seem to be hungry; all I can say is, he's fine and very healthy so we don't bother stressing about it any more.
It can be frustrating when you have kids who are reluctant to eat much - WE want them to 'please, just eat a little bit' of something, ANYTHING, you know they would probably go for a bag of crisps but you don't want them to just eat junk. This little ParentHack could be worth considering and may solve the lack of eating problem, even if only on the odd occasion (kids!).
It's ever so simple - use various shaped cookie cutters to cut out shapes in either bread or toast; you can make shaped sandwiches which, somehow, sometimes, seem to be much more acceptable than the very same sandwich when it's square.
I'm not a huge fan of messing around massively with food a'la Big Cook Little Cook, but I'm all for throwing those 'principles' out the window when needs must!
If you've found ways to navigate the rocky road of reluctant eating, do let us know so we can share them with other parents.