"Mullin said Allen told police he saw three girls on the bridge and was “looking at his stock ticker.” Allen then said one of the girls “appeared to be older” and that she was “babysitting.”Walking by he Dldn't see or register the 9 yo in favor of noticing the teens.

Delphi Murders trial: Day 6 live blog
Delphi Murders trial continues with testimony from Dr. Roland Kohr and Sarah Carbaugh. Allen accused of murdering Abby Williams and Libby German.

So he did see, but either got his number wrong or he just didn't include the small child.