In terms of drop-ins on Mon or Tue, I know of the following...
Baby Group for parents, carers and babies - toddlers.
Church hall next to St Aidans school on Stapleton Hall Road (next to the YMCA nursery). Not quite Crouch End I know.
Monday mornings 9.15 - 11.15
£1 per child
Baby group run by the Church staff, tea and biscuits available.
If you wanted to come up to Finsbury Park, there is also Jamboree, in the Play Huts in Finsbury Park (nr the entrance on Seven Sisters Road)
Every morning 11-12.30 and then again in the afternoon 1-2.30. FREE. No need to book
Toys, books, crafts, things like water and sand play. Outdoor play too. Good for toddlers.
You could also try the drop-in at Stroud Green Childrens Centre on a Monday morning, which is also free but no outdoor space. Probably worth also investigating Campsbourne Childrens Centre if that is near you.
NCT playgroup, as suggested by Elkiedee, is probably your best bet as it is quite cheap but still has lots of toys and indoor and outdoor space. And cars, which you specifically wanted!
- Bumps, babes and tiddlypeeps
CUFOS, Top of the Avenue N10 (between the playground and the Laboratory Spa)
Tuesday 3-4.30
£1.50 per family group
Soft toys, puzzles, pretend play, bikes and outdoor equipment, arts and crafts, Usually a singsong at about 4.00ish.
Good for toddlers especially. Homemade cake usually available (included in the entry price).
And finally, don't forget...
Singing with Jeremy
Mon, Wed, Fri 10:30 - 11.15 Priory Park Cafe.
£3.50
HTH.