Hi Maine,
We went to Petra on Lesvos about 8 years ago. It was lovely, very traditional and the people were sooo friendly. We often played cards with the locals on an evening. It still rates as one of the nicest holidays in Greece we've ever had. I still remember my hubby's face when we went out for dinner on that first night - we were invited into the kitchen of the taverna to pick what we wanted - he'd never been to Greece before and couldn't stop telling people about it when we came home
From what I remember, you should find it child friendly. It's got a lovely long seafront, ideal for pushing the baby. The beach is great and the sea was quite calm. Most places to eat had tables outside so can sit with baby in the buggy by your side. The Greeks seem to love kids so I'm sure they'll make a fuss over her.
I'd recommend climbing up the the church on the hillside to watch the sunset one evening, it's lovely.
I believe that there has been some building in the time since we've been but it's still one of the best places to go for that traditional feel.
If you are getting the coach supplied in a package deal, do be aware that it's quite a drive BUT it is worth it, however you might want to get a taxi to save the hassle.
If you fancy a change one day you can catch a taxi to Molyvos which is the next town along - it's very pretty.
Hope that helps.