Yes, the Heys would hold your diapers and such, but not a lot of mom's things with the diapers.
Right now I have both a Baggallini Messenger bag and a Heys Travelmate. I filled both with a couple of water bottles (for weight) and wore them around the house while doing my housework. Bending, squatting, etc. I wore them in the front and the back, and each was comfortable.
I chose to keep the Baggallini because of it's size. While I'm sure I won't fill it up, I like to have 'wiggle' room. Extra room so I'm not having to remove things to find what I'm looking for. Room for those 'extras' I pick up at the parks, which I felt the Heys didn't have (for me). Also, I feel I have more versatility in carrying options with the Baggallini. And the flashlight didn't work on the Heys bag

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I got both bags for around $20. The tag on the Heys says $39.99. There's NO WAY I'd pay that!