I don't know where to ask about this, so I thought coming here... someone in BakaBT should know

I was doing the exercises about adjectives (みんなの日本語一, 第8課

) when I stumbled upon the 小さい and 大きい adjectives. There they are like い adjectives, but I remembered listening somewhere to 小さな and 大きな (like in the Clannad song, 小さな手の平, lol). So I searched in the kanji book and there it says:
大(おお)きい=大きな
小(ちい)さい=小さな
So, it's the same to use them as い or な adjectives? Or are there cases where I have to put 小さい and others 小さな?