Although both sentences get across the meaning, neither is completely natural. The first is OK, definitely the better of the two, but I at least would rephrase it: "Children gawped at the cattle which for the first time after winter leapt outside from the barn," putting "for the first time" before "winter".
Otherwise, your written English is very good; your punctuation is of a very high standard, apart from the first sentence, which is a question and should have a question mark.
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