I had a similar situation with my soon to be 10 month old. She is used to falling asleep on her own no cry, no fuss, after our little routine; but for a couple of weeks she just would take longer to fall asleep. Not only that, she would wake up at 3-4 am and play (her night light lets her see pretty well) and would be up a good hour and a half to two! During all this, I was going crazy, not sleeping, all the while she was perfectly fine... sleepier during the day, but nothing else. I noticed the night waking was happening, she was also developing some new skills- standing all by herself, saying some words (well, trying to say... mama, papa, aga for water and tete for milk- we speak Spanish at home). In due time, she started to sleep a full night again.
I do not recommend you going in unless they are calling you or crying. That is extra stimulation for a mind that is already looking for a reason to stay up. If there are no signs of illness, this is probably just a developmental phase and with all other phases, this too shall pass.