Worried about lack of babbling at 8.5 mos

Hi there,

Totally new to this forum and hoping that the members here can help me out. My DD (I think I used that right!) is a happy, healthy 8.5-month-old. Very speedy physical development - she stood today without support for about 2 second (not long, but it was a first), has been pulling herself up on furniture for about 2 weeks and "walking" inside her crib by hanging on to the railing. Sits up on her own and has for a while; still does army crawl most of the time but has been getting into a "all-fours" position more often. Born at 39 weeks but was on the small side (5 lbs, 10 oz) and is still in the 20th or so percentile for length/weight. Social, smiles at people, makes good eye contact (though occasionally looks away, especially if something more interesting catches her eye or if she is overwhelmed), responds to her name. What I'm concerned about is that she doesn't do the "canonical" babbling I'm expecting and have read is normal for this age. She makes lots of vocal sounds, like a high-pitched squeal, a "raspberry" sound, a sort of buzzing "b," a "bobo" occasionally, a "mmmm" and "agoooo." But not the babababa, dadadada, mamama I've been waiting for. Should I be concerned? Sound familiar to anyone? I confess I'm sort of hyper-vigilant about noticing anything that may be a red flag for autism, because I know how important early intervention is. We've been using baby sign language with her for the past six weeks or so, and she does seem to wave now with some regularity with it would be appropriate (e.g., when someone new arrives). She's also not had any "stranger danger" yet and tries to get the attention of strangers to interact with them.

Any thoughts? I'd love to hear your experiences.

Many thanks!