I'm having this same issue. Here's my save folder. In this house the sim named Shayna can interact with the toddler no problem and vice versa but the one named Jaycee cannot pick the toddler up and the toddler cannot interact with Jaycee at all. I tried the switching into disguise and this gave the toddler the option to "call over" Jaycee but when I then tried to get Jaycee to pick her up the issues came right back and the switching in and out of disguise did nothing after that first time. Whenever I tell her to pick the toddler up this is what she does and then the action is cancelled out.
Edited to say that the problem fixed itself somehow the next sim morning(or at least that's when I became aware that she was able to pick up her kid and the kid could talk to her again).
