Hi, in my opinion, if a cashier talks to customers in casual / informal way in Japanese, it sounds a bit impolite in general. We think you are not their friend, but they are your customers. If I were you, I would never have the casual conversations with them. After you become their friend, it depends on the relationship between you, but before that, I'd like to recommend you to use the formal form. 

If you write down the phrases in English, I'll try to translate them into Japanese if I can with my English. 

I see, I thought you wanted to talk to your customers who are adults in the casual way, so my suggestion didn't make sense.

To communicate with small children, I would use there following phrases: 

こんにちは (Konnichiwa = Hi / Hello) 

なんさい？ or いくつ？(Nansai? or Ikutsu? = How old are you?)

(for girls) かわいいおようふくだね。かわいいおくつだね。

(Kawaii oyoufuku da ne. = How sweet / nice / beautiful your cloth is!

Kawaii okutsu da ne. = How sweet / nice / beautiful your shoes are!) 

(for boys) かっこいいシャツだね。かっこいいおくつだね。

(Kakkoii shatsu da ne. = How cool / nice your shirt is!

Kakkoii okutsu da ne. = How cool / nice your shoes are!) 

(If they have something sweet / pretty / beautiful, pointing it) かわいいね。

(If the have something cool, pointing it) かっこいいね。

(When they are leaving) またきてね！(Mata kite ne! = Please come again!) 

(To their parents, you should use the formal way) 

おはようございます / こんにちは / ありがとうございました。

I hope this was helpful. 

I beg your pardon? Why would you say that? I hate no one because of their race.

Do you hate Chinese people?

Hi! Thank you for your comments! There are only a few customers and they do especially two with their kids like to speak to me in japanese, though I can only say a few sentences. I dont consider us friends ya know just friendly service ^^