Kids entertainment

I think a space with different board games would be great - you can have some for all ages (candy land, snakes and ladders, scattegories, crazy eight deck, boggle etc). If you check with your bridal party/parents etc they likely have some you can borrow. I second the idea that a lot of parents will bring something to entertain their kids but I'm sure they'd appreciate a dedicated play space.

I imagine the older teens will likely have phone/ipads but may be entertained by the board games if there's enough of their age group to play

Bouncy house or inflatables! Some places offer deals/discounts for these events. I only found this out as someone suggested it for the actual wedding. And most of them have someone from the company supervise the activity during the rental. Which means parents can enjoy their time!

We just had colouring available for them. Most children are able to entertain themselves for a few hours. Maybe have some games available for during the dance. Honestly, most parents will bring something for their children (phone, ipad probably!)

A goodie bag for every child can be given out and have small blocks or dollar store toys to be played at the table. Lego is also good for those who will want to make more as a group.

I don't have many kids coming, but I am having Wedding themed Mad Libs on the tables for children and adults alike to do if they don't like dancing.

Also a DIY photo booth is fun. Just go to the the local thrift store and pick up a few wacky items, and place them somewhere in your venue with a blank wall. The older kids can help the younger kids and adults can enjoy it too! All they need is a cell phone with a camera

I would go to the Dollar Store, as well as WalMart... just browse the kid sections for inexpensive goodies, it's hard to list many of them, as they are kind of random. You can definitely do colouring, suitable for all ages, get some of the adult colouring books, or just print a few more complex colouring pages for the teens.
The younger teens will be able to join in for the dancing, and will actually probably pay attention for many of the games/speeches.
Also, many parents plan for distracting their kids, from colouring to electronic devices.

I heard colouring books are good. For the older kids the adult colouring book stuff is more for their age.