Sim can’t interact with toddler

Try it without mods, but generally, yes, toddler interactions can be frustrating. Especially the high chair. To quote my description in the bug report forum:

You: Put toddler in high chair.
Sim: Picks up toddler. Puts toddler down next to high chair.
You: NO. Put toddler in high chair.
Sim: Puts toddler in high chair. Immediately takes toddler out of high chair and puts toddler on floor.
You: (#@*$#%&. PUT. TODDLER. IN. HIGH CHAIR.
Sim: Picks up toddler. Puts toddler down next to high chair.
You: I'm going to kill someone in a minute. Seriously. Don't even. PUT. TODDLER. IN. HIGH CHAIR. YOU. STUPID. (#)$*#&$!
Sim: Puts toddler in high chair.
Second Sim: Immediately takes toddler out of high chair.
Popup: [Toddler] is very hungry! Make sure you feed them before they're taken away!
You: (#@*$#%&. PUT. TODDLER. IN. HIGH CHAIR. *scream of frustration*
Sim: Picks up toddler. Puts toddler down next to high chair.

Repeat until you give up and cheat toddler needs.

But I digress.  😉

Also, sometimes if your Sim's home is cluttered they can't route properly to do some actions. Are you playing in a "strangely empty" EA home, a cluttered gallery home, something of your own devising...?

In other words: it can be a lot of things, including broken mods, bad pathing, or just the general bugginess of some interactions.  (My least favorite is when I ask the toddler to grab food off the table and they just stand there starving because their parent on the other side of the house has the action "put toddler down" queued so the toddler is waiting for their parent to hike over, pick them up, and immediately put them back down before they'll obey your instruction to eat.)