Starling I've felt this way in the past. Sometimes the decluttering has to be gradual and it's not possible to do it all at once. I'd start with a favourites box, for the things you'll keep forever as a memento. Then go through the rest for anything too worn to donate which needs to be recycled and put it straight into the recycling, even if that means driving somewhere to do it, otherwise you'll end up bringing it back inside again. Put your favourites box away somewhere, you've chosen them so you don't need that again. Maybe that's enough for the first time.
Next time whenever you want to keep something tell yourself you already chose your favourites and stored them, be strict with yourself. Go through all the general things that don't have sentimentality eg multiple plain vests or babygrows and bag them for donation. If you've somewhere to donate them take them straight round so you can't change your mind. If you're planning to sell as a bulk lot then set aside somewhere.
Now it's just the difficult stuff, the pretty things perhaps with a degree of sentimentality but not enough to be your favourites. Try to shift your mindset. You have your favourites. Your house is not a museum. You can't display everything, there's no room. All these things will do is hang around forgotten, they won't get looked at or appreciated. It's almost a crime against the clothes and their services to you to keep them hidden away, stuffed in a bag, languishing in a corner forgotten somewhere.
Is there anyone in particular you can think of who'd like this or that? Gifting feels like a kindness, not loke the disposal of getting rid, and you have the pleasure of seeing another child wearing it.
There's places that'll turn old clothes into teddy bears if a relative needs eg a birthday present. Or you could do it and give it to your own child when they're older.
Could you do with the money? Is there anything in particular that would sell well? Pick out those pieces and advertise. Do one at a time if it feels emotional so you don't get overwhelmed.
Put the rest with the plain stuff you bagged earlier, knowing that it'll help the plain stuff sell and get you a few pennies for something else, perhaps a photo frame for a favourite pic of your DC? If you're donating them then take them straight away so it's done and you can't sneak them back in the house. Remind yourself you have your favourites.