I do some, but they usualy have so much homework from school that they don't
have time when I am at home.  They do TaeKwonDo after school.  Often I do
go jogging/weights/sprints with my oldest son.  My 3 year old loves when I
do weight lifting with her as the weight.  She also sits on my back while I do 
pushups.

Still, the most frequent excersize is alone late at night.  In the winter it is 'invigorating'.

R. Keene