This would be a two part answer!
First, I don't know if you go to church or not, but ours certainly has lots of activities for kids starting with Palm Sunday tomorrow. Because we're Episcopalian, we have services on Maundy Thursday and Good Friday, but more adult than you might look for. A church in your area might have children's services during the week and especially on Easter Sunday. Since this is Holy Week, and all about the Resurrection, some service somewhere should be part of your Easter celebration.
As for more "fun" stuff, I always dyed eggs (you know, the old fashioned kind from chickens, NOT plastic) with the kids. Sometimes we used the packages from the grocery, sometimes just food coloring with vinegar to dye eggs. You can paint them, but maybe make when they're over. The Easter Bunny then came and hid them for the egg hunt Easter morning. We also made Jell-o eggs in the molds you can sometimes find from Jell-o (that would be the more concentrated form of gelatin that stays solid).
Baking special cookies or hot cross buns is also fun, and 4 is a good age help Mom cook. There is bound to be some activity somewhere in Houston (I live in Austin) like a neighborhood egg hunt or egg roll that you could go to. You don't say if they're girls or boys, but going to a craft store and getting a hat and decorating an Easter Bonnet is fun also.
Enjoy the holiday with them, but be sure to tell them the reason for it.
Christ has died. Christ is risen. Christ will come again.