Not sure how to feel about this

Kai got his 18 month checkup today. He's only mumbling the words mama and daddy when I guess he should be saying atleast 5 words by now. So, they are sending him to speech therapy because they would rather catch any problems now than later. I keep thinking that he is just slow to talk and he'll do it eventually. But then there is part of me that notices his obvious frustration when he can't communicate what he wants from me, and that's hard on both of us. It's just this feeling...like you want to think your children are in the 90th percentile of everything and then wham...there's a part he's well below average in. I know I shouldn't be worried or even think too hard about it, but I'm a mother and I overanalize everything when it comes to my kids. I'm sure it will be fine.......I hope.....