dads incubators got me interested but to learn i had to start with blinking a LED wich at the time seemed boring and a waste of time, was only after i learnt a fair bit that the value of making a Led blink became apparent, i take the point of quad copter so maybe line follower? you can start with led for that, how many weeks you got? as for where would i start i would start with motor control by pwm. but ok quad copter out, main point was you need something that will get attention from the start, telling them they will learn to blink a Led will give you alot of time on your own
as for where to start with flow code i have no idea i have never used it, but i do know someone who was on here learnt from zero knowledge to making a cool aquarium controller with all the bells and whistles including backlit rgb lcd with zero programing knowledge to start with and he used flow code and by the end could tweak it with C , so its got power and apparently easy to use. so with a tight amount of hours like yours it would it the bill of doing something fun to do but without spending huge amounts of time learning a language, no one is going to learn basic in 5 weeks with 4 hours a week and do a fun project.
but you are the teacher and i am the kid so go with what you think is best, i only try and give you a look from a kids view point but again its no longer valid as they are alot older than me, as for my copter i will use accelerometer and gyro and do it in C18, i am only learning C slowly but i have time and it gets easier the more you do.
if you can teach anywhere near as good as those that teach me on here then it will be a success, without the guys on here i would still be blinking a bloody Led!! lol