Besides the obvious answer (the park), you can check with your local zoo and see if they have any free days or reduced rates on certain days (since the kids are so young they may be able to get in free!, just pack a lunch and all you will have to pay is admission). If you DO go to the park, take some bread along to feed the birds (kids love it!). You can also pack a picnic and take it along. You can also take a book about birds and see what birds you can spot or flowers, or whatever is your fancy. Here is a website I found that has some activites I found too... http://www.savvysource.com/activities/browse_1a_3-4_years_activities