Kylie Jenner and baby Stormi stole the spotlight at North West and Penelope Disick's birthday party.

Kim Kardashian West and sister Kourtney threw a lavish unicorn-themed joint party for North - who will be five on June 15 - and her cousin Penelope, who turns six on July 9.

However, it was Kylie, 20, who turned heads as she brought along her four-month-old daughter - whom she has with her boyfriend Travis Scott - in a Gucci baby-carrier worth $700.

Sharing a photograph of herself and her tiny tot on Instagram, she wrote: ''happy birthday North & P.. (sic)''

'Keeping Up With The Kardashians' star Kim - whose daughter North is the eldest of three children she has with her husband Kanye West - posted pictures from the party on Snapchat showing North and Penelope in matching sparkling rainbow robes.

The children could ride on ponies dressed up as unicorns with coloured horns attached to their heads, which Kim joked were ''real unicorns, guys''.

The party food included a unicorn cake, unicorn-shaped ice-creams and cookies, a rainbow Maypole and elaborate table decorations.

The two birthday girls played in a pool filled with inflatable rainbows and entertainment was provided by DJ Livia, a 10-year-old DJ who previously appeared on 'The Ellen DeGeneres Show'.

Guests included Kim and Kourtney's grandmother MJ and family friend Larsa Pippen.

Penelope is one of three children Kourtney has with her ex-partner Scott Disick.

She and North now traditionally share joint birthday parties. Last year there was a 'Moana' theme and they have previously shared a Mermaid party.

While Kylie was celebrating her nieces' birthday party, she missed her brother Brody Jenner's wedding in Bali.

The 34-year-old model tied the knot with fiancée Kaitlynn Carter but revealed his sisters Kylie and Kendall had snubbed his big day.

The hunky socialite said previously: ''My two little sisters, we never even heard from them. They never even RSVP'd I don't think. We sent them an invite but we just never heard anything back. Well, they'll be missed. I would have loved to have had them there.''