I have a 4 and 7 year old. Each of them have their own devices. Obviously it costs more. My two often end up fighting over something if they don't have their own, and with the cost of this product it was worth getting two. They both sit with each other and play and show each other what happens. My 4 year old has this, and my 7 year old has a WolVol tablet that was $99 and runs on Android.
If I were you I would n't buy two of these. There are quite a lot of variety in Apps to satisfy both 3yr and 5yr olds provided you spend a lot as most of these cost $20+ a piece. Note there's no WiFi in Leappads whereas their competing device InnoTab2 has secured WiFi, can play mp3/mp4 etc
I probably can't help you with this, i have 5 year old twin grandsons, and therefore had to buy each one of their own. I gave them to them this weekend and my personal opinion after seeing the games is that i would not buy it for a 3 year old.