Same issue here. Playing on PS4. Both parents are adults and cannot assist with most toddler activities. Luckily she’s about to age up, so no potty training still needed.
I tried multiple things. Dollhouse, for example, if the toddler clicks on it and chooses “Play with...” and selects a parent, she will then go play at the dollhouse, but the parent will never join. If the parent clicks dollhouse and the “Play with...” the same thing happens, toddler goes there, parent doesn’t move. While playing at the dollhouse a toddler used to be able to click on an adult and say something like “ask to join playing dolls,” and the adult would run over to play. That dialogue option is gone. Even tried this with Patchy, since he’s played with kids before, but still not an option. (I think he’s marked as young adult?) Also, used to be an option if the toddler was already playing the parent could click dollhouse and hit “Join,” there is now no ability to even click if the kiddo is already there. Same basic thing with the blocks except the parent will walk over to the blocks, just won’t do anything.
Not sure if it is somehow related, but the “Play with...” option is also missing from our chess table for the child sim. Didn’t mess with that one since he doesn’t need to play chess rn anyway. Just was clicking around on other things where that was an option before to see. Water balloons “Play with” function worked fine.