what does the below rebus means?

Two fathers and two sons decided to go to a shop and buy some sweets upon reaching. Each of them bought 1 kg of sweet. All of them returned home after some time and found out that they had 3kg of sweets with them.

They did not eat the sweets in the way, nor threw or lose anything. Then, how can this be possible?

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

There are 3 apples in the basket and you take away 2. How many apples do you have now?

We have shown you a regular water barrel as below. Without using any measuring device can you check if the barrel is more than half-filled or less than half-filled?

Get total of 120 by using five zeros 0,0,0,0,0 and any one mathematical operator.
Do you ?

It has a long neck, A name of a bird, Feeds on cargo of ships, It's not alive,

What is it?

The dirtier I get, the whiter I look. Who am I?

John was running from 40 thieves. John has got 3 gold boxes which weigh as 4kg, 2kg, and 1kg respectively. A witty man asked John to stay with him for seven days in exchange for 1kg gold per day. John needs to stay there for seven days and also do not want to give the witty man any advance. How can John pay for his seven days stay?

The centre of the third figure is empty. What digit should fit inside?