What does toys r us actually sell? Can you actually get everything in one place?
I would just put some money in a pot each week at home, mid December you can decide what to get based on how much money there is.
How old are your children? What type of thing are they looking for?
I wouldn't by anything 'gymiky' that they only will use a few months max. Buy stuff you can see them still using a few years away. Lego is a good one, craft bits like nice watercolours can be used at home and for school work, etc etc
In my children's stockings I try and stick to:
Something to wear -( this year long sleeved Tshirt and slipper socks)
Something to eat -( prob Lindt reindeer and satsuma)
Something to read -( roald Dahl book and small travel book)
Something to play - ( travel game and skipping rope)
It's an easy and practical thing but if you cover the above they will have a selection of items and some will save you buying after also as practical. You can get more of each if that's your preference.
Ask kids to write a list of 10 things and say you will try and pick at least one as main present, tell them what rough budget is so no Apple Mac airs appear!