On child income section, what is difference between ordinary dividend and ordinary dividend received as a Nominee(included in line above)?

Nominee Dividends are dividends reported to you that belong to another individual.  If the child received ordinary dividends that belonged to someone else, that is what you would report as Ordinary Dividends received as a Nominee.

what form are you looking at? For practical purposes for the Kiddie Tax, which is what I think you're asking about, there is no difference between ordinary dividends and interest incme. However, qualified dividends get special treatment. TurboTax should ask about them.