It is said by a boy who has just finished talking about his plan to a group of little kids. Here is the sentence.
とまあ ざっとこんなところだが どうだみんな！
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It means somethng like "So, ~~" used when trying to wrap up a convo or explanation. It is mostly an attention-drawer than a meaningful phrase.
The 「と」 is, believe it or not, a quotative particle used to refer to the over-all content of the speaker's statement that is now ending.