De or het lottoballetje?

The correct Dutch article is:

het lottoballetje

Rule Diminutives (-je, -tje, -pje): always het. See the rule

How to use lottoballetje

the lottoballetjehet lottoballetje
this lottoballetjedit lottoballetje
that lottoballetjedat lottoballetje
our lottoballetjeons lottoballetje
your lottoballetjejouw lottoballetje
every lottoballetjeelk lottoballetje
which lottoballetje?welk lottoballetje?
a big lottoballetje / the big lottoballetjeeen groot lottoballetje, het grote lottoballetje