My DD did this at about the same age. Normally not a fussy eater but for a while, a long while, turned her nose up at everything... or say she was hungry then only eat about 2/3 bites and then stop. I didn't make an issue out of it because I thought that at the time it was attention seeking. What I did was make chocolate Sustagen milkshakes for her when she got home from school and was the most hungry. I added a scoop of ice cream to make it irresistible. She always drank them so that was a consolation that she was getting most nutrients. After a while her appetite picked up again and now she eats more than me, easily! I'm not sure if the improvement after the Sustagen was just a co-incidence but it worked.... didn't have to buy a second tin. She asked for the school sized Sustagen drinks which i bought her for a while to have occasionally as well.