I noticed something similar in Dec 2021 when I visited. I don't have kids but I wasn't super hungry so I was planning on ordering a kids meal. I wanted the potato base but couldn't find the kids potato base as an option on the app. I ended up just getting the adult portion because I really wanted the potatoes but I thought it was odd. We mobile ordered but if I was really adamant about it I probably would have just ordered in person because I'm sure it's something they could accommodate. I'm assuming it's just a glitch so if you still don't see it when you arrive just order in person. But for what it's worth it wasn't a huge portion anyway.