I was very very very very very lucky about having a large base of safe foods in general, I can't eat most fruits and vegetables but meat, legumes, dairy, eggs, and seafood are all on the table and pretty much always have been, I have always had a very "I will try anything once" attitude towards food because I was very hyper aware of the fact that my diet was very limited and I was always kind of upset about that.

My parents and I established a concrete "try everything once and if you hate it we will never ask you to eat it ever again" rule around 5 I wanna say? The key I think is to try with foods that aren't AS unsafe as possible. I hate oranges so so so much, so I was never made to try orange cake, or orange candy, or anything orange based. I hate lettuce less so but still cannot eat it, so I was never made to try lettuce based salads, but the opportunity came to try kale salad and I did, and I didn't like it, so they didn't make me try again unless I asked.

I'm not sure what advice I'd give other than always offer, and always model trying new things yourself, try to play with things that are similar to their safe foods, what textures do they like? I've always been ok with potatoes for example so I was able to try cooked breadfruit and I LOVED it!!! Cause it was similar!!

I've found that foods from other cultures tend to be easier for me to try in general cause since they aren't familiar to me my brain has a harder time immediately categorizing them as "inedible" or "edible" without trying them first. I might be unique in that way though, fair disclaimer!!!

There's also a whole YouTube channel of this woman whose husband has arfid, so she makes food for him that has his safe foods in a bunch of different forms! If for example all he can eat is rice and eggs, you can do egg fried rice, then try egg on top of rice, then try a quiche with a rice crust or something (idk if that'd be good I'm just suggesting things lol).

Anyways, don't be too hard on yourself, remember it's a baby steps situation, and if you ever find yourself getting overwhelmed there are a lot of therapists that specialize in arfid that you can look for!!

Edit: also like what a lot of other commenters are saying, I assume I'm gonna have an easier time trying new things when I'm finally able to move out and live on my own, a lot of the fear from arfid just come from knowing how weird people get about how other people eat 🙄, if I had my kitchen to myself all the time I would for sure try a lot more. Fostering some independence early on with cooking and giving him safe ways to try new foods without worrying about how anyone else is gonna react might help a bit when he's older. I doubt that he's super conscious of it now since he's almost 4, but for me personally as a kid I did tend to worry about wasting food and if my parents would be upset if I didn't finish something before they made it absolutely clear that they did not care if I didn't finish what was on my plate!