Please don't flame me for being worrying FTM. I know milestones are approximate but Everything I'm reading (my baby books and apps) say purposeful smiles happen Around the 6 week mark. LO was born 5/10. I've seen little smirks but I don't believe the big baby smiles I'm reading about has happened yet. LO makes tons of good eye contact and is physically very strong. How old did your LOs give you their first big real smile?
Re: Smiles...
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I'm no expert, but try not to get overly worried at this point. I guess if it really does become concerning you could consult your pediatrician.
My LO is 5.5wks and I've been getting the big smiles around 4wks. I also put my knees up and lay LO against them and just talk to him. I ask him about his day and we talk about the crazy dogs. And that's where I get my big smiles and little giggles. Maybe try that.
Honestly, professionally speaking- it is more about the joint attention (evident by eye contact) more than smiling. You can have a stoic yet neuro typical child. There is such a range of normal- really, the technical milestone for intentional smiles isn't 3-6 months of age, and some babies do it faster.