We have a new friend tonight to join us...,

[Silverobama]

Last night at an English club for kids, a little girl came and join us. It was her first time to be there. At the beginning of the meeting, I said to everyone “We have a new friend tonight to join us. Let’s warmly let her introduce herself. Applaud!” Is my sentence natural?

 

[emsr2d2]

Last night at an English club for kids, a little girl came and joined us. It was her first time to be there. At the beginning of the meeting, I said to everyone “We have a new friend joining us tonight. to join us. Let’s warmly let invite her to introduce herself. Applaud Please give her a round of applause!” Is my sentence natural?

See above. Saying "Applaud" in the imperative isn't appropriate. It sounds like an order!