ANi,
Our daughter drinks a big glass of milk in the morning and then have her sip into a bottle of water on the way to the hospital. we generally do the blood draw early morning...when she was young, we used to wrap the area with a mitten to keep the hand warm. ALso, the nurses always used a hotpad for few seconds before poking. Also try to keep your child calm during the poking. I have seen when our daughter is very agitated, not all nurses can keep calm and do a good job the first time.
regarding the amount of blood, i think your child is gettign less ...generally the rule of thumb is below 9.9 Pre Tx Hgb, the child shoudl get 20/kg (i think it is cc not exatly sure)./ between 9.9 and 10.5, it shoudl be 15cc/Kg. if the child is always coming at 8, you should try the 20cc/Kg first before reducing the Tx frequency lower.
we have never used Heparin so I can't comment on that.