Excuse me, but this is Kids Plate. Is that all right with you?
まず、Excuse me, but ... (失礼ですが...)で始めましょう。
Excuse me, but this is Kids Plate.(失礼ですが、これはお子様プレートです。)
「それで大丈夫ですか?」は通常なら
Do you really want it?
Are you sure it is what you want?
のような言い方がありますが、この場合はやや直接的すぎる感じを持たれかねないので、
Is that OK[all right] with you?
Are you happy with that?
といった表現の方が柔らかくなります。