Kidʻs love to receive notes. Even better when it is a surprise. Try writing a note in Tongan and leave it in your kids lunch box if they are old enough to read. As you incorporate more Tongan words into your childrenʼ vocabulary and/ or yourself, they will soon learn to love speaking in Tongan. You could expand this to suit your circumstance. The possibilities are endless.
The picture above was a note I wrote for my eldest daughter. It was her first day back at school today. She started year 2 or second grade. I have noticed she is speaking a lot less Tongan since beginning primary (elementary) school. So I try to incorporate more of the Tongan language where ever I can for her.
I wrote a little note ʻofa atu = love to you. I thought she might have problems reading it but the love heart gave it away. Her reaction after school was worth all the effort
Tu’a ‘ofa atu
Let's learn Tongan 
Malo mu’a tokoni lahi ‘oku ma’u ‘i he website ko ‘eni. Ko e ki’i kole ke ke tokoni mai keu lava ‘o ngaue’aki ‘etau ngaahi faka’ilonga fakatonga, hange koe toloi mo e fakamamafa pau.
Viliami, vakai’i atu e peesi oceanicorthography he tohi’ata (Facebook) ‘oku ‘i ai e tongan keyboard te ke lava ‘o download ‘o ngaue’aki.