I was helping a friend of mine plan a party for her 9 yr old who loves Lego building blocks. I told her to use a picture from the Lego site to make her invites.For decor  Use small balloons and stick them to the same colored paper forming lego's all over the place.I told her to use a white plastic table cloth to cover her birthday table with.Use plastic cups dipped in different color paint to make round lego marks on the table cloth.By stamping out rows of 4 across and 3 down you should have what appears to have big lego's on your table and you can have your kids help do this. Use colored plates and cups making things very colorful. For the cake Use a plain white sheet cake and place some lego's on the cake in the shape of the yr your child will be.When the guests arrive give them a sheet of paper with the A colored lego on it( Red,Blue,Green etc) Tell them to remember the color as they will need it for a fun game.One of your activities will need to be prepared ahead of time. Use tin cupcake pans and fill them with water. Use anything that has a shape and fill it with water. Freeze these items until solid you can add food coloring to the water to turn the shapes different colors if you wanted to.When frozen run the molds under hot water to loosen the ice from the form. Get a bag of plain ice cubes or make them yourself again add color if you want. Get those spray bottles out either you have some or will need to by some. When the kiddies arrive have them go outside and sit at a table or on your patio and bring out the fun. First give them those stretchy gloves they can be found at walmart for about $1.50 for a two pack. Hand each child a bowl full of different shapes or let them pick there own out of the many you might create. Tell each child there going to make there own Lego ice sculpture using the spray bottles to stick the ice together. They can make anything they want and Moms this is great for those hot summer days or even in the winter time. Just think the Ice will melt leaving no mess and fuss and the food coloring is non toxic so even the littlest party guests can join in the fun.One of the games you can play next is take a big tub of your legos and pour them onto the floor then tell the kids to grab there color only ,the one they got from the card at the start of the party. Tell them they can make something neat and you will give out prizes for most creative at the end of 10 mins or so but tell them only to use the color you chose for them( Make sure ahead of time those colors you give out match the ones that are in the tub) Goodie bags are the easy part. Make a Lego pinata using a medium cardboard box or the newspaper paper mache. Fill the pinata with small lego's or medium ones and candy. Have the children take turns hitting the pinata till it breaks and then give each child there goodie bags to fill there bags. Have extra candy and legos on hand for the kids that could not fill there bags up.For Thanks you cards dont forget to take a picture of your child with there lego Ice sculptures and say thanks for the cool Gift.