Both signs contain the warning in hiragana あぶない with the latter adding emphasis with
あぶないよ!both of which mean 'dangerous or watch out'.
The top sign uses:
池(いけ)- pond
The bottom sign uses:
柵(さく)- fence
Both signs use:
の中(なか)に - in the/to the ...
入らないで(はいらない)- do not enter/go in
ください- please
ね - 'ne' is a confirmation ending like saying, 'eh' or 'right'.

As you can in this picture if the warning is ignored it may cause significant damage to your body as there is no water in the pool!!

以上です。またね。
ジョシュア