HELP! Wet weather plan for Christening needed

[LadyMuck]

Ds's being christened shortly. My plans relied on fine weather. We have approx 40 kids coming (7 under 1s, majority seem to be age 3-7, but a dozen or so from 8 to 15). Also 50-60 adults. Original current plan was to have it at home - bouncy castle in garden, someone doing kids food, finger buffet (a la Waitrose) for adults and any interested kids. Plenty of room, and also possibly larger than usual selection of stuff in garden (climbing frames, sandpits, bikes, football etc).

But can't fit everyone in if wet. Have a church hall as back-up, and catering transfers easily, but what to do with kids? Could a children's entertainer work? Any ideas please. Assume shortish notice but money no object (short of flying everyone somewhere warmer). Christening is in Croydon, but we live about 4 miles away, so assume everyone has car transport for that sort of distance.

HELP!

Measure the ceiling height of the church hall and make sure that you have a bouncy castle or ball pit that will fit into the church hall too.
Have a large box of colouring stuff, duplo, cars, car mat.
Could you have a word with a couple of parents of the older ones to see if someone would bring a portable tv, playstation and some suitable playstation games.
By the way, I think this is an excellent idea. A friend had a bouncy castle at their wedding - kept the kids amused for hours.

Thanks. I'm trying to get hold of caretaker to see what would fit. Do you think that would be enough to take care of the kids - my eldest is 3, so don't yet have much experience of entertaining older ones, though a bouncy castle has seemed to keep most of them happy for barbqs in the past.