、。
Mommy, that boy just totally wiped out!
Literal
Mama, now that brother amazingly fell-down [emphasis-よ].
Child speech again. あのおにいちゃん ('that big brother') is a warm way for a small child to refer to any slightly older boy. すごい in its casual あたりし variation すっごい/すっごく emphasizes 'really, super.' ころぶ ('to fall, take a tumble') in casual past ころんだ. The sentence-final よ added by a child has an emphatic, alerting tone ('did you see that, mommy?').