Getting someone to hide a weapon from the police has become an offence under measures brought forward after a spate of gang-related shootings.
Guns removed from circulation by the Metropolitan Police
Ministers say the act gives police throughout the UK strong powers to tackle gun and knife-related violence.
Adults who use children to hide guns will face up to 10 years in prison.
Other powers coming into force on Friday under the Violent Crime Reduction Act target mobile phone and alcohol-related crime.
The new weapon-minding measures mean that it is now an offence to get others to carry or hide guns and knives.
They aim to target gang members who seek to avoid prosecution by getting other people to hide their weapons.
Those found guilty of using children to hide firearms face a sentence of up to 10 years and those using minors to mind knives will face up to four years in prison.
People using other adults will face a maximum jail sentence of five years.
At the same time, the range of offences for which an offender can be given a mandatory minimum five-year sentence is being extended beyond just simple possession of a banned firearm.
The sentence will now apply to offences including:
- Possession of firearm with intent to injure
- Possession of firearm with intent to cause fear of violence
- Carrying a firearm in a public place
- Trespassing in a building with firearm
Home Secretary John Reid announced in March the measures were being moved forward after a summit on gun crime.
Five south Londoners, including three teenagers, died in shootings earlier this year, prompting pressure on government to act.
Mr Reid told BBC Radio 4's Today programme the new measures would be used alongside putting more police on the street and giving extra resources to community groups.
"When we get the use of knives by younger people, or guns by younger people, we need to strengthen the police presence in the streets, we need to strengthen the communities by giving money and resources to voluntary groups who are trying to tackle gangs and guns and knives," he said.
But he added the new offence of using someone to hide or carry a weapon was also important.
"One of the things that people who are using these knives do is get younger people to hide them, and of course they can then escape that offence if they're not caught in possession," he said.
But Liberal Democrat president Simon Hughes told the BBC unless the government "dealt with the causes" of gun and knife crime it "probably wouldn't solve many of the problems".
Another new measure detailed in the act attempts to crack down on child alcohol abuse.
If a minor is sold alcohol in a licensed premise in England and Wales three times in three months, the licensee will face prosecution.
They could have their licence suspended for three months and be fined up to £10,000.
And a new UK-wide law banning the reprogramming of mobile phones is coming into force.
This measure is designed to target the black market in stolen phones.
Criminals who have stolen phones reprogrammed to sell them on now face a maximum sentence of five years.