Taking DS to playgroup, rhyme time, kinder gym was definitely out of my comfort zone. I'm not very social IRL and don't enjoy small talk with strangers, etc. I'm guessing it's a whole different level for you DE rather than just being a bit shy.
Honestly, the first time will be the hardest and it will get easier. The great thing about going with your kids is you can just talk to them and follow them around. If you do get chatting to some other mums I'm sure they will surprise you with how lovely they are. I don't know what it's like with your SN kids, but I find DS is often moving onto different things really quickly so I hardly have time to hold a conversation with anyone, which is brilliant.
Good on you for pushing yourself. It will be worth it