The first molar comes in next, at about 14 to 18 months. However, this tooth is not right next to the front teeth. The canine tooth is the tooth that appears between the front four and the first molar, but it comes in after the first molar, usually about three months later. Thus it is perfectly normal to see a toddler with four front teeth, then a space on both sides, and then a "back tooth" on each side.
I am not sure from your description if this is what your child has. Athough it would be unusual for your child not to have the lateral incisors if he already has his first molars, it does not mean there is a problem if he does. As long as the appearance of the teeth is normal, and the gums are healthy, a slight change in order of appearance should not cause you to worry. Once your child has the full set of eight top teeth and eight bottom teeth, there is usually a long wait until the second molars (the two year molars) appear between 24 and 32 months of age.