Activists, physicians, and social workers urged lawmakers Tuesday to expand a state welfare program helping low-income parents, arguing existing cash grants are insufficient to meet growing costs and leave many children stuck in poverty.

After helping this year to repeal a law preventing families on public assistance from receiving additional benefits when they have another child, activists now want to secure further changes through a bill (S 36 / H 102) that increases support offered through the Transitional Aid to Families with Dependent Children program.

Rep. Marjorie Decker, who authored the House bill, called it the “next step” for lawmakers after lifting the so-called “cap on kids” law in April.

“With the grants we provide, people are really treading, they’re treading water,” Decker told the Joint Committee on Children, Families and Persons with Disabilities. “And let’s be honest: some people aren’t treading, they’re drowning. This is really just about throwing them a life jacket and letting them hold on and take a breath.”

The grant amounts have not changed since 2000, Decker said, and their value has declined since 1989 due to inflation. An average family of three currently receives $593 a month, just a third of the federal poverty level.

“We talk to families all the time who are struggling to survive on this,” Naomi Meyer, an attorney at Greater Boston Legal Services who helps lead the Lift Our Kids coalition, told the News Service ahead of the hearing. “It is simply not enough.”

The legislation, which already has more than 100 sponsors across the House and Senate, would increase the value of the aid every year until it reaches 50 percent of the federal poverty line, the threshold marking “deep poverty.”

Decker said the change would cost the state about $15 million per year, but said the investment would also help avoid higher costs down the line because it would ensure better outcomes — and therefore fewer urgent services needed — for recipients.

About 29,000 Massachusetts families, including 52,000 children, currently live in deep poverty, a number that bill co-author Sen. Sal DiDomenico called “staggering.”

“These families need our help,” he said. “These families have nowhere else to turn. These families are on the edge of despair. And these children who are in these families are growing up in a way where they have no other idea of what living a normal life looks like.”

Advocates rallied at the State House Tuesday morning before the bill came up for a committee hearing, where they packed the room wearing matching Lift Our Kids vests.

Pediatricians and psychologists focused closely on the children who would benefit from greater state aid to low-income families. Seth Kleinman, a Danvers school social worker, said children who live in poverty are often “completely unavailable” for education because of hunger, stress and other social and emotional issues.

“Being focused on the classroom is far from their top priority,” he said. “Poverty really has myriad impacts on them.”

During Tuesday’s hearing, the new proposal also had Republican backing: Rep. Michael Soter, the committee’s ranking minority member, said he “proudly” supports the bill, even after taking “a lot of heat” for his vote in favor of the cap repeal.