Talk to them before you start the shoot and the parents. Find out about
something that recently happened that might be funny or talk to them about
something they like. They'll smile.

that age group can be really easy.   Call them Mr President, Mr Astronaught.
Mr Fireman, kids of that age eat that up, especially boys.

Or just call them the wrong name, changing it each time,  Jim, stand right
there, (ah, my name's Joe)  ok Jeremy, put one hand in your pocket, (no my
name's Joe)  fine Jason, turn your head this way.   Girls seem to fall for
being called a boys name.

kids just can't help smiling.

for a hard a.s,  of almost any age, I'll pause, and with the pose set and
camera ready, I'll look at them, and deadpan, almost seriously,  "well,
don't look so mean and nasty"  and 99 out of a hundred they will give you a
brilliant smile, I mean it works on gang bangers, all but the most
professional poker faces.   Its something genetic to disarm a potential or
unintended threat.

Tell them you will take away their birthday if they don't.

Word has it that on Sat, 11 Oct 2003 16:45:44 GMT, in this august forum,
"Steven Church" <s.church@snet.net> said:

Smiling (not leering!) at them, then making funny faces or noises often
works. They have to be relaxed though. If the child is nervous or tense,
you're out of luck. Don't let mum or dad try to pressure them into
smiling, because it just makes things worse.