How can I make my middle child feel special?

My son was telling me in school they had to say why they were special. I asked what did he say and he told me he did not think he was special because he was not one of the big girls (his 3 old sisters) or one of the babies (his three baby siblings). I tired to explain he is special that he is nice to Snappers (his turtle). He is a good swimmer and he can draw well. But he just shrugged his shoulders and said I guess like I was lying to him. And not that I think of it he does kind of get "ignored" because the oldest girls have activities that I have to get them to, my youngest are just babies so they need a lot of attention, and i figured since he was there with us that he felt important. So what can I do to make my little prince feel like a king?