It is common for children in this age group to be fussy about what they eat. Due to growth spurt, they often appear thin but as long as they are maintaining adequate weight for their age, there is no real cause of alarm.
A 4.5 year old should ideally take all home based foods and avoid carbonated drinks, excess chocolates, candies, concentrated juices which can result in what we call Toddler's diarrhea
Give him plenty of cereals and fresh fruits and 2 glasses of milk every day apart from his daily diet. Give him eggs in whatever way he likes, either boiled or half fry. And do not worry about his hyperactive behaviour. Only if the problem persists, you show him to your Pediatrician
I hope I have answered your query.