I have 34 babies who started hatching on the 24th of June and the last hatched on around the 26th... So that makes them about 9 to 11 days old, similar to yours
It seems unusual that yours have been alive so long and you havnt seen them eating, its quite noticable as they jerk upwards and forwards when they are catching the BBS, and then after about 15 mins they should have quite plump little orange bellies, and its all visible to the naked eye. I sometimes use a torch on the darker babies if I'm unsure whether they have eaten, there are also 3 of mine that were born a lot smaller than the rest and 1 that has a noticable deformity in regards to the shape of its head and spine, and then there are 2 who appear normal and who I do see eating, but for some reason their bellies don't appear very big or orange like the others - and they are growing at a slower pace. The 3 tiny babies are all eating and catching up to the bigger lot so I think they are normal, just small, and the one with the deformity eats like a pig and is growing so I am letting it try his/her luck at survival, but maybe your babies are like the last two I mentioned who look normal but who don't seem to get orange bellies... they eat but they aren't as savage as the others and I have to watch very closely to make sure they do, and they are starting to fall behind growth wise... I'd say if they weren't eating anything at all then they would be dead by now, unless they have hatched prematurely and are still digesting their yolks and living off of that. Can you see the yolk in their bellies if you shine a torch over them? I noticed that my premature babies that hatched first took longer to start eating because they digested their yolks, where as the later hatchers had almost already done that and were ready to eat within 24 hours and at the same time the prematures were ready (which for them was around 2 to 3 days of not eating what I offered)
Is this your axolotls first spawn? Because apparently sometimes babies in first spawns sometimes don't develope properly or as typically as those born from mums who have spawned before. Although if your babies are still alive after 9 days and definatley growing (mine are noticably bigger now and are close to getting arm buds) then I'd say they should be okay as long as you keep up with the BBS and the water changes
have you checked to make sure your BBS are moving around/nice and active