tomato plants

I planted some tomato plants back a couple of months ago in the greenhouse to which I have since re-potted a few weeks ago.  They are currently only about 4 inches high. Is this normal for this time of year or should they be a bit taller now.  I am going to re-pot them in a week or so in to larger buckets as ther final location within the greenhouse.  Any tips and advice would be greatly apreciated to if I am doing anything wrong or should be doing to the plants at this time of year.

thanks for the advice.  Luckily they seem to have picked up now and are doing pretty well. Not sure if they are as big as they should be as yet prob around a 15" high so far.  The next question I am wondering is should I start to remove some of the lower leaves to allow the plant to grow taller and start producing flowers?