Yeah, in a few years a PS3 might be wonderful for them but by the time they're old enough to actually enjoy a PS3 it will also be much cheaper. Kids 10 and under love them some DS's so the more DS stuff you get them the more they'll love you. If you get them a PS3 there are a few games they'll enjoy but they will likely go back to their DS.
My sister has kids that are 9, 6, and 5 and they have a PS3, Wii, and thee DS's. You know what gets played the most? Their DS's by far. The TV generally gets stuck on some kid show and they play their DS. Buying them a PS3 at this moment would be a cool gift but would end up just wasting your money.
See, that's why I had dueling TV's in my room. TV shows on one TV.
NES/Atari/Balley Astrocade/SNES/ETC on the other.
Or games hooked up to both in the case of a lot of company.
Before i moved out to Vegas I actually had a 3 TV setup. Atari and NES on one... 360 and Wii on another... and PS3 on the third. That was fun. Helpfull to if there was a basetball game I wanted to keep my eyes on.