I personally have never been to a Lego Party, but it sounds like a lot of fun.
If there is not a private area for the party, have you considered just having the party somewhere else - home or somewhere there is a lot of room for the kids to play then providing the Legos yourself? How long can the kids play Legos before they will get bored? This way if you purchase the Legos yourself your son gets to keep them to play with all the time and still enjoy them at his party.
By the way if you need any entertainment for your party, my husband and I are professional clowns living in Anna. We offer facepainting, balloon sculptures, comedy magic shows,friendship bracelets, along with fun interaction and games. We've entertained at birthday parties and large events like the Plano Balloon Festival.
Our prices are very reasonable (we have four great kids of our own so we know how expensive things can get)and we do our best to work within a person's budget.
Please feel free to take a look at our website at www.freewebs.com/bubblesandwowza for samples of our work.
Give us a call at ###-###-#### if you have any questions at all.
Hope you have a great party whatever you decide to do.
Hope to hear from you,
Bubbles the Clown
Bubbles and Wowza, LLC