The plan was for our youngest to use the stroller. He was a few months shy of 3 years old. The problem was that he refused to sit in the stroller. There's no way to make a child to sit in a stroller who refuses. He refused to walk too. Luckily, I had brought my ring sling, and so I carried him using that. It was out of practice after a year of not wearing him, but we managed. Though I used the ring sling, I've heard the Ergo is better for toddler wearing.
The next year, bribery finally worked to get him to sit in the stroller, so I didn't have to carry him. The next year, his sensory issues actually made him want to sit in the stroller though he had to be carried in lines. (It was his sensory issues that had him refuse the stroller in that other trip).
*I used the ring sling with my first child until 16 months old easily. He was 33 lbs then. It was actually much easier with a slightly heavier child who was older due to how the weight was spread out. However, me being out of practice muscle-wise was an adjustment.