Thank you all for your help. I solved the issue by taking the previous save, before the girl turned into a toddler, clearing my cache and removing all custom contents. I did not really use it anyway, they were just attached to Sims I had downloaded from the Exchange; and since I did not need extra households given that Union Cove is already well populated anyway, I might as well do away with them.
I guess that's a lesson learned and that I should always look twice when adding stuff from the Exchange, people are not always clear with the content they include in the download.