I would get the double. Our son is 3.5 yrs older than his sister and from when she was I can't remember 6-9 months old they shared our double trailer until he grew out of it (his head didn't fit in anymore) around age 6. Then she had it to herself until she was about 6, for the same reason. Even if you don't have a 2nd (or more) kid(s), the extra carrying capacity is always handy. We used to stack groceries around one or both kids until the trailer was just full (subject to the 100# weight limit, we found they really meant that)