Dentition on infants
Infants generally start getting their first teeth in sets of two starting at around 6 months, and every two more teeth every two months till they have all 20 baby teeth. So, at 6 months they generally get their first two, at 8 months they'll get two more, at 10 months two more, ect. Apart from the general fever and malaise that this will give young babies (as any parent can attest), this is the time to stop letting kids sleep with milk in their bottles and it's the time to start developing brushing habits before going to bed. So, brush those two little teeth (tooth paste really isn't necessary at that age) and if they absolutely need to sleep with a bottle, make it water. Milk will cause early childhood caries, which is a heart breaking problem and never easy to fix.
As to when you should bring them in, compliance is the key. Kids ideally should get checked as soon as the first tooth come out by a pediatric dentist. In our office, kids can usually stay still in the dental chair at around 2 and a half or 3 years old, so that's when we generally see them. Of course, every kid is different, but that's a good rule of thumb.
Hope that helps and please call us if you have any questions!
Dr. Lopez and Dr. Gely