Ideas for 4 year old birthday party with younger siblings to consider.

[GetToFalkirk]

Every year since she's been born we've had a joint birthday do for my DD and her friends, whose parents we made friends with at the antenatal classes we took.
This has been no problem so far in finding things to etc, however this year we have to take into consideration the younger siblings who range from 1 - 2 yr olds.
We were thinking about going bowling but this isn't suitable for the younger ones who just want to run about.
We are all on a tight budget so hiring a hall etc is out of the question. Their birthdays are in October so we are limited to doing indoor things.
Last year we did a Thomas train trip, the year before that we did soft play.
Any ideas please?

.

I would say bowlings ok. We're having a bowling party for my 5 yo this yr and his 2 yo and 9mo siblings are attending.

How about swimming? Or going to a place where u paint your own pottery (our local place has pieces starting from £2). What about a visit to a local farmpark? Going on a boat trip somewhere? Or a zoo visit?