can the age of childsupport be increased from 21 to 23 ,since my children will still be in college.

Generally, the answer is no. You may be able to get child support until the child turns 22, if enrolled in a full-time college program. Also, if the other parent agrees to extend the support, you could always agree to that - but it seems unlikely. Talk to some attorneys near you to get a more detailed answer. Good luck!