At what age wa your child communicating in sentances and counting to ten and is my daughter behind?

I think my boy is probably gifted. He is certainly exceptionally smart. The problem is that it is prejudicing my essment of my daughter. He could not only speak in structured sentences at fifteen months, but could count 1 to 10 at less than 17 months. My Girl is now 19 months. Although I don't think she has a problem she is so far behind where he was it is difficult not to worry a little. She seems to understand ever so much but only has a vocabulary of around 30 words. At her age my boy had a vocabulary of over 1000 words. Unfortunately I am now separated from my partner which means we jointly spend with her less than 10% of the time we spent on him. Is he just distorting my expectations or should I seek advice?