I feel like I'm doing something wrong

I am a mom of two girls, one is 2 the other turned 1 yesterday. When my oldest turned two she got referred to early intervention because she only says a total of 5 words. (She didn't qualify because she excelled in other parts) She is now 2 1/2 and can say maybe 3 or 4 more words but shes not quite where she needs to be. My youngest had her 1 yr doc appointment yesterday and she doesnt say anything. Now she's been referred to early intervention as well. I just feel like I'm messing up since they aren't talking like they should and I feel so stressed about it. I read to them and sit and talk to them but it just doesn't seem like anything is working at this point.