Jack has spent nearly every second of his life within 11 feet of his mother. Throughout the story, we've seen this separation anxiety from Jack. For example, when Ma is having her first shower, Jack is with her. At first, Jack doesn't want to get in the shower (an example of his disposition against change). When Ma gives up on getting Jack into the shower, she shuts the door so that the water doesn't leak out. Unable to see his mother, Jack panics and hits the door to get it open. In addition, he's also crying, showing the emotional turmoil he is going through (Donoghue 172).
This separation anxiety will be something Jack needs to overcome in the future (ex. when he leaves for school, etc.).
What's less obvious though, is Ma's separation anxiety from Jack. Although it isn't as obvious, there are some signs that Ma is extremely attached to Jack and worried about him. When they first arrive at the precinct, Ma asks for Jack to stay by her side the whole time. When her parenting is questioned, she gets defensive. When talking to her father, she says that "He's [Jack] the world to me," (Donoghue 226).
Sure, Ma's separation anxiety isn't as bad as Jack's, but I believe it'll take time for her to become comfortable with Jack being independent. Up to the point we're at in the story, Ma has literally spent 5 years of her life taking care of Jack, and most importantly, protecting him from Old Nick. We see her become super protective of Jack whenever Old Nick is around, telling him not to touch Jack or look at Jack. She will almost certainly carry these protective instincts with her on her return home.
Ma even explicitly states that she needs to work on being herself again, instead of being Jack's ma.