ばかりでなく

ばかりでなく means "not only… but also": X holds, and Y holds as well. It follows a noun directly, the plain form of a verb or an い-adjective, or a な-adjective with な, and the second half usually carries も on the added item.

A noun takes no な or の before it, and a な-adjective needs its な.

• × 子供のばかりでなく → 子供ばかりでなく
• × 静かばかりでなく → 静かなばかりでなく

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ばかりでなく sounds a little formal and turns up more in writing. In conversation the same thing is だけでなく, or だけじゃなくて among friends. ばかりではなく, with は, means the same.

ばかりでなく or ばかりか

ばかりか has the same shape but goes further: the second half is something you wouldn't have expected, and it often carries まで or さえ. ばかりでなく simply adds one thing to another.