Thanks all. Money isn't so tight that they won't get anything new, they already have some new things hiding at their grandparents' houses. I just thought that with the already huge pile of toys they already, it would be good to buy some secondhand things to save a little money. Especially DS's clothes since he's 9 months old and outgrows them weekly.
DD already goes through her toys once a year in December and donates toys to the pediatric department of our local hospital. They sterilize them and use them in their playroom. She has also gone through her toy boxes and took out all her baby toys for DS. She knows that's part of Christmas.
Thanks for all the replies. Now I don't feel so bad while scoping out the online swap and sells.