It's the opposite. Usually babies don't eat any food at 4 months. They only get breastmilk or formula. The advice is to start early with peanutbutter and egg.
In our case diary products were an issue instead of nuts. My daughter would get very sick from anything that had diary in it, even if my wife ate diary products while breastfeeding. But at about 1.5 years one she got over that and now at 4 she is completely fine drinking normal cow milk.
So allergies in kids are not a permanent set in stone thing. They can get over some, and early exposure makes a difference.
No, it's the opposite. The advice we were given was that it was very important that their first encounter with the allergens was to eat them, and not to allow skin contact or anything before that. This meant that with my youngest we had no peanuts in the house until she was old enough to eat solid food, and peanut butter was the first food she ate. It's still her favourite food!
If you're avoiding skin contact, then you might not have time to wipe the peanut butter mess off your hands as you rush to rescue your kid who's got into trouble.
It wasn't about them not being in the house - it was about not eating them, and particularly not feeding them to her 2 year old sister. We didn't throw them away - we just didn't buy any as we weren't going to be eating it for a while.
Babies change fast. I can certainly imagine it. You won't know when exactly the flip happens, so you err on the safe side. Also, spread of stuff though the air and by hands: I thought we just spend lockdowns realising that crap spreads far and wide.
I am not sure if you had a child or not, but you don't give the baby food before 4 to 6 months. So its not that you aren't exposing them at all, but not feeding them the food.
There are powders to add to your formula / breast milk to introduce allergens early (we used Ready Set Food but easy to DIY). Kind of annoying since they often clog the nipple of the bottle, but we did it with my daughter who is now 20 months and her favorite breakfast is a spoon of peanut butter. Sesame gives her a slight reaction still, we unfortunately don’t eat it very often.
I'm assuming you're not a parent, but it's a valid question! No food before 4 months, babies can and should subsist on breastmilk or formula before that.
What goes wrong if they're exposed before that? If the mother eats peanuts and eggs while breast feeding, does that confer desensitisation?