TG and Thais in general are very kid friendly.

However your two children being already 8 & 11 (toddlers/lap children would be another story) I can not see how they could be accomodated in a (full?) cabin with only 8 seats. Even sitting on the ottoman during meals is not an option as the FA would have to provide food for 10 people.

Even if the FA would not object, I think they could run into trouble wih other guests and it is probably also against the procedures.

I think the only option is that during take off and landing one parent is with one child in Y, the parents have then the main meal together in F and for the rest of the flight it is again one parent with one child in Y.