I know that there are a lot of kids that IMO are way too old to need a stroller. That being said, you should be careful with the judgements. My DD will spend a pretty good amount of time in a stroller this trip and you would probably think that she looks perfectly normal and too big. The thing is that 1. she is very tall for her age. She just turned 4, at her check-up they had to get out the 5 year old growth chart just to chart her and she was still in the 97th percentile. 2. She has autism. While she will walk a lot of the time, there are times that she is going to need to put on her headphones, sit in the comfort of the stroller and get a sensory break.
My point is, you can't always tell by looking what is going on.