I second the "yes" comment. Assuming your 13 month old isn't a giant, it should be perfectly fine to share a seat. Buying a separate seat will be even more difficult unless your child is the type that listens to every instruction from the parents. I think the only challenge is during meal times (for you) but that can be worked around. Don't expect to be super comfortable since your child's comfort will take priority but it is much better than Y!