そんな言いい方かた、子供こどもっぽいよ。

sonna iikata, kodomoppoi yo.

Saying it that way is childish. casual

彼かれの考かんがえ方かたは少すこし子供こどもっぽかったです。

kare no kangaekata wa sukoshi kodomoppokatta desu.

His way of thinking was a little childish. neutral