need ideas for kids craft at family reunion

You could buy a bunch of little wooden birdhouses or trinket boxes, etc. at the dollar store, and a few bottles of craft paint and some inexpensive paint brushes and have each child paint and decorate one for themselves. You'd have to have a table big enough for them all to be seated [or stand around] and maybe take an old sheet or some newspaper to cover the table first. Save up your little plastic containers from fruit cups or yogurt to put the paints into. Then all you would need is some water in plastic glasses for rinsing the brushes in between colours. Oh, and maybe a roll of paper towels would come in handy. Ask parents to bring an old t-shirt of theirs for a smock for their kid. If you wanted to get fancy, you could also bring some white glue and sequins for decoration. The kids could put the glue on with toothpicks and then stick on the sequins after the paint is dry.

Tie dyed t-shirts

Paper plate masks? Using paint/pens/crayons/glue/paper/sequins/beads/wool/fabric/lollie sticks etc to decorate. Pasta plates - dye dried pasta shapes various colours and the children stick the shapes to the plates to make pictures. Or thread the shapes to make necklaces, bracelets etc..

What about some wooden letters with family last names? Will you know in advance who's coming and can you plan for that?

You could put the names on picture frames or on a wood block somehow.

Maybe make a door hanger with name letters?

Be use it's a reunion, I'm
Stuck on names LOL!

Have fun!

Clay flower pots.  We did that one year for our family reunion and the kids had a blast.  They also got a pack of flower seeds for their pots.  

Another craft we did one year was t-shirts.  Parent supplied a pre-washed shirt and the kids were given fabric paints, brushes and shaped sponges to decorate with.  If you do this be sure to have some cut-up pieces of poster board to slip inside the shirt so the paint doesn't bleed thru.