They can handle a full grown mouse at that size but besides the risk of the mouse injuring the frog, nutritionally it is not good to feed that size of mouse to that size of frog. Now if your pixie was 8" vent to snout it would be fine. But it just has to much fat, protien and fur for a 4" frog. A small hopper might be ok but like SCF said you might wanna kill it before you feed. I used to hold the mouse down while my frog attacked its head but that is not a good idea i got bit a lot by the frog and I will tell you what you dont wont to get bit by these guys. PM me if you want good methods on killing the mouse before you feed. It is a little graphic to post on a thread.