Three nights per week or every two weeks? The first is about 43%, the second is about 21%, big difference. If she has nearly equal time and your incomes are fairly close it may be okay to just let it go. (I just peeked - 3 nights per week. You get ALL weekends? That's very unusual! No court would have ruled that way, but they'll let it happen for a settlement where you both agreed.)
Did the order already include some financial reimbursement terms such as for medical, dental and school expenses?
If you immediately ask for child support, could it trigger her to go back to court and want a redo? For that reason I'd hesitate to act too quickly since you don't want her to rush right back to court seeking to change it all before it has become the "new normal". (And the "new normal" might be the kids spending even more time with you than listed in the agreement. So keep documenting. It may not affect any child support calculations since they typically depend on the order, not the reality, but document anyway just in case you do end back in family court. For many of us it's a revolving door as repeat litigants.)
Another factor is that neither you nor your ex knows what your financial circumstances will be in the years to come. What if you have a major accident and your income drops? What if she remarries and she moves into a house three times the size of yours? If you delay asking for child support now, are you legally able to ask for it later?
Warning! Feelings of guilt. If you feel badly, take the money and put it in a trust fund for college.
This is an excellent method to defuse claims of you taking advantage of her, abusing her, etc. Yes, you saying you're reserving it for the kids won't impact her resentment or her perceptions but using that logic when talking with court, the various agencies or with
reasonably normal people will help show them you're not vindictive or unreasonable, that you have the children's interests as your priority.
