Dd is 7 months and has never put things in her mouth. She will happily pick things up and play with them, bang them, pass them back and forth etc but she shows no interest at all in putting them in her mouth.
She is fine being fed by me but won't try to put the spoon in her mouth. If I give her a piece of fruit or a rice cake, it gets played with as if it were a toy but it never goes near her mouth.
She is a thumb sucker from the minute she was born and will lick things that are within reach of her tongue, such as the zip on her coat, but just doesn't bring things to her mouth.
I know people will say I'm lucky because I don't need to keep an eye on her all the time, but I am a bit concerned.