you can play with your toys when you've got changed
「おもちゃで遊ぶのは後にして」= you can play with your toys later / you can play with your toys after your bath / you can play with your toys when you've got changed
「おもちゃで遊ぶ」= play with (your) toys
「お風呂の後」= after your bath
「着替えの後」= after you've got changed
もう既に回答は出ていますので、同じ状況で使えるフレーズをいくつかご紹介したいと思います。私も子供に向けてとてもよく使います(笑)
It's not playtime anymore.
もう遊ぶ時間じゃないよ。
No more playtime.
遊び時間は終わり。
Not now.
今はダメ。
You have to take a bath first.
先にお風呂に入りなさい。
Put your clothes on, then you can play with your toys.
洋服を着なさい。そしたらおもちゃで遊んでいいよ。