Appreciate ID Help: Central NJ Brook / River finds

[Jawamac]

Item 1 looks like a pretty large bivalve, but maybe it's just a rock with a cavity or seed pod? Item 2 seems like a fossil to me, and seems to have the right "look" of a fossilized bone. Item 3 was found in the same spot as 1 and 2, a fallen tree next to a creek in Southeastern Mercer County. Item 4 was found farther south in NJ, near the Delaware River in Burlington County. My 10-year old is convinced it's a fossil - the blue rock is very soft, the matrix seems to be reactive to vinegar.

 

As a beginner with a youngster who is obsessed at the moment with finding fossils, I'd love to be able to confirm we are heading in the right direction - even if we can't positively identify. And if these are just rocks, that's totally fine too  The fun is in the hunt and spending time together. Thank you for lending your insight. Really.

[Fossildude19]

Sorry, but I am not seeing anything fossil related in the pictures.

[Plax]

My guess is that 1 is a bog iron concretion known as an Indian paint pot in some circles. Number 4 looks like modern concrete with coarse aggregate.

[Jawamac]

Thanks so much for the confirmations!! Agree and appreciate it!