Gone are the days when a sandwich, bowl of jelly and a game of pass-the-parcel were enough for a jolly children's party. Social media bragging and peer pressure have upped the ante.

Some parents admit to spending £800 on their little one's birthday bash, with £300 being the average cost, according to a poll by Mums Show Live!, an exhibition for parents with children between four and 12 years old running in London from 16 May.

"The pressure to spend and throw elaborate parties is a growing trend – and one which parents are struggling with," says Siobhan Freegard, founder of website Netmums.com. "The pressure isn't coming from the kids, but the parents."

Extravagant parties include an entertainer for three hours at £435 (£145 an hour); catered food and drink for 30 at £3.95 a child (£118.50); hire of a hall at around £100; birthday cake £64.90 and party bags for everyone at £3.25 each add up to £97.50. Grand total: £815.90.

One mum on Netmums recently moaned she had to do it three times over – goody bags at school for the 30 pupils in her daughter's class, a children's birthday party, and another for adult friends and family.

Justine Roberts, Mumsnet.com founder, says: "Peer pressure reaches fever pitch and it can be a battle to keep expectations and costs down."

Here are simple ways to stop your party parting you from you money.

Invites

Email invitations or download them for free from websites such as Netmums.

A fun idea from Mumsnet is to write the details on an inflated balloon, let the air out and ask the nursery or school to hand them out after class.

Share the party with one of your children's friends with a birthday around the same time and keep it short, say two hours rather than three. Keep numbers down by making it clear that guests' brothers and sisters aren't invited.

Venue

If you can't face having it at home, or don't have enough space, summer parties can be held in a local park or free outdoor play area with a picnic and energetic party games.

If you don't want to take a risk with the weather, get a quote from a soft play centre or local hall. Avoid peak times – weekends, school holidays and half terms – when admission charges are higher. Babies often get in for free. Ask if you can bring your own food.

If there is a play centre or child-friendly cafe near you, try to do a deal. Investigate offers for children's parties on parenting sites such as Likebees and Littlebird, suggests Netmums. Or go to a Saturday morning movie where tickets can be just 99p.

Entertainment

Professional children's party entertainers are expensive. There are horror stories of the family pet savaging the magician's rabbit and little ones being left in tears by grumpy clowns. Keep the stress and cost down by doing it yourself.

Mums Show Live!, at London's Alexandra Palace, is running clown classes for parents on how to entertain a bunch of boisterous youngsters. Classes include magic tricks, balloon modelling and face painting, as well as tips for making children laugh and what to do when they cry or misbehave. Alternatively, you can always organise traditional games such as blind man's bluff, pin-the-tail-on-the-donkey and musical chairs.

Cath Harrop is already thinking ahead to her son Freddie's birthday party in July when he turns five. She didn't find three-year-old Alex's birthday in April too demanding, but Freddie is in reception, and she'll be inviting all 30 children in his class.

"Last year we had a pirate-themed birthday for Freddie at home," says Cath, who lives in Wimbledon, south London, with her husband Simon, "but we can't have 30 children in the house."

She's looking for a local hall and plans to share the event with one of Freddie's school friends. She's also signed up for the clown class with some friends.

"The thought of standing up in front of a bunch of children terrifies me, so I'm hoping the class will help me with crowd control," says Cath, a former doctor, who now sells second-hand children's clothes and toys through her company Mum2mummarket.co.uk.

"We've been to some fabulous parties where they've hired entertainers costing £300 an hour. The party bags are a headache, too. People put more and more stuff in them. A lot of it is rubbish.

"Last year I did all the food, made the cake and decorations and Freddie's party still cost about £300 – though we did have an entertainer dressed as a pirate and a treasure hunt."

Catering

Young ones typically don't eat much, so don't go overboard. Sandwiches, crisps and ice cream with a flake should be enough. Or ask family and friends to bring a dish and bake your own cake.

If you're not a baker, and don't know an enthusiastic amateur, buy plain fairy cakes and get the kids to decorate them.

Borrow a tablecloth and decorations from a friend. Or get a plain white paper cloth, scatter crayons and stickers on it and get the children to draw on it. Balloons are always popular, especially if you customise with glitter.

Party bags

These are a real bone of contention and thinking up what to put in them can be stressful. Even if you buy loads of plastic toys from a pound shop this can quickly add up.

One idea is to buy a set of books such as the Mr Men series and let the children choose one to take away. A book will last far longer than a tatty toy that will be broken by bedtime. Or do a lucky dip.

If you must have a going-home gift, decorate brown paper bags and buy seeds, multipacks of sweets and stickers to fill them and a slice of cake. Or fill a jar with sweets and tie a ribbon round it.

There are lots of ideas on the internet on how to throw a great party on the cheap. The mums' websites have chat rooms where you can ask others for tips. Also look at party sites, such as partydelights.co.uk, where you will find plenty of goodies to buy.