Smash cake icing?

So baby hasn’t had sweets yet, only natural sugars like fresh fruit. I’m doing a smash cake with a muffin recipe he LOVES. Carrot, zucchini, banana, & oatmeal, I know he’ll prolly eat it all if I let him 😂 I’ll be doing a two tier 6 in cake. My question is what should I do for icing??? I don’t want it to have added sugar but understand if that’s the only way to make it happen. Any mommas found a good recipe or alternative like a yogurt based frosting? Please share your ‘unsweet’ 🤷‍♀️ “frosting”. TIA and all suggestions/variations are welcome!