With our DS5, we haven't done anything formal yet. We basically just follow his lead as to his interests. What does your DD like to do? We do experiments in the kitchen, he creates things with his legos (i think he finally has enough now that we've run out of room for them!) We play board games with him. He likes blokus and chess right now. He likes to sit around and make designs with pattern blocks.
He liked learning software for awhile (like jumstart), now we let him do webkinz, where you can earn the most "webkinz" cash by playing games.
As for things outside the house, we go to children's plays, and read the related books ahead of time and talk about them. We go to science museums. He's in a gymnastics class. We're hoping to start him with piano lessons soon.
If she likes to write or wants to learn math, you could get some workbooks. DS5 doesn't really care to do them.
We'll be looking into summer classes this year too, since DS is now 5. There are usually some fun-looking classes at the science museum.
We continue to read to him every day. Have fun with your DD. I think it's hard to plan anything too far ahead for these kids -they sometimes quickly change their interests or move beyond what you thought would be good. I wouldn't recommend buying presents early and stashing them!
