The background is quite nice, the angle is a pretty good choice for mom (I suspect she doesn't want her bottom half emphasized in photographs -- most women don't!)
She has a pleasant expression, but it looks a little bit like a "cheese!" smile, a pro-forma smile for the camera, not a genuine smile. The little one's pretty funny, I like the wide-eyed "WHAT!!!!" expression. I'd have tried for more genuine humor. Keep shooting, crack a joke, catch both of them off guard in a "moment" when there's fun in their eyes, that sort of thing. Quite possibly you did take a whole bunch of photos, and this was the best of the lot, and sometimes that's just how it goes.
The light is flat, there's very little modeling on her face. Direct sunlight is too harsh, usually, but perhaps there's a time of day when the light sneaks in here a little to light up their faces from the side a bit?