Elopement wedding in London with kids - what to do after?

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Having a small registry / elopement style wedding in London with 3 young children. I want to do something after the actual wedding (with the children), any ideas?
We could sit down to eat somewhere nice but it inevitably won’t be nice after about 30 minutes and I don’t want to ruin a nice day. I’m thinking something to do / some kind of activity? I don’t mind throwing a bit of money at it. A big wedding is not my thing at all but I want something special to remember the day by.
Any random ideas?

Firstly how old are your children? Secondly what are you planning to be wearing? Something like GoApe might not work well in a wedding dress!

How about one of the old route master buses that you can do afternoon tea on?

Go to a matinee performance at the theatre?

London is a big place! Depends whereabouts!

River cruise?

Hire a London eye pod and have champagne? Champagne bar at the top of the Shard? Helicopter? Speedboat on the Thames?

How old are your children?

See children are young, the speedboat thing has a height restriction. The Shard and London Eye don’t. Don’t think the helicopters take children under 4 years.

Meal somewhere fun then a trip down the Thames- stay in Greenwich?

Not wearing a wedding dress but will be in heels and a skirt looking nice-ish so can’t really run around!

Young kids - and youngest not even walking. Older will be happy with some kind of “vehicle” based thing and I’m googling things around going up places for the view and going on buses and things but I’m finding that often the choice seems to be between an “engagement”/ hyper romance “package” that wouldn’t be suitable with kids (and anyway it’s not an engagement) or just being one of a crowd up the Shard and I think I’d feel a bit overdressed.

It doesn’t need to be really romantic. We basically consider that we’ve done the wedding already a while back but getting round to the legal bit. At the same time, I want a nice day I can look back on fondly.

London Eye?

London Eye always has a wedding party on it on a Saturday, always dressed up! It looks great!

Mad Hatters a afternoon tea? https://www.morganshotelgroup.com/originals/originals-sanderson-london/eat-drink/mad-hatters-afternoon-tea?utmsource=Google%20My%20Business&utmmmedium=Website%20Button&utmcampaign=London